Islamist fighters march during a graduation ceremony at a training camp near Damascus last month. They were to join the Ahrar al-Sham Brigade. Reuters
The U.S. and its allies have held direct talks with key Islamist militias in Syria, Western officials say, aiming to undercut al Qaeda while acknowledging that religious fighters long shunned by Washington have gained on the battlefield.
At the same time, Saudi Arabia is taking its own outreach further, moving to directly arm and fund one of the Islamist groups, the Army of Islam, despite U.S. qualms.
Both the Western and Saudi shifts aim to weaken al Qaeda-linked groups, which Western officials now concede are as great a danger in Syria as President Bashar al-Assad's regime.
Some officials in Western capitals remain wary about courting these groups, whose ultimate goal is to establish a state ruled by Islamic law, or Shariah, in Syria. Throughout the conflict, the U.S. and its allies have balked at sending powerful arms to any Islamists, fearing such shipments could end up in the hands of al Qaeda-backed forces.

The Main Syrian Opposition Alliances

The U.S. and its allies are shifting to talks with some Islamist rebels.
  • Free Syrian Army An alliance of moderate rebels led by Gen. Salim Idris. The FSA has lost ground and influence over the past year. Once thought to include up to 150,000 fighters, commanders say it now has about 40,000 men.
  • The Islamic Front A new coalition of militias with the goal of establishing a state ruled by Islamic law in Syria. The group, which commands about 45,000 fighters, has recently attended talks with Western diplomats, including the U.S.
  • Al Nusra Front and the Islamic State of Iraq and the Sham These groups, designated as terrorist organizations by Western powers, have ties to al Qaeda and are shunned by the West. They want to establish an Islamic caliphate in the region.
Source: WSJ reporting and IHS Jane's Terrorism and Insurgency Centre.
The Saudis and the West are pivoting toward a newly created coalition of religious militias called the Islamic Front, which excludes the main al Qaeda-linked groups fighting in Syria—the Nusra Front and the Islamic State of Iraq and the Sham, known as ISIS.
Over the past two months, the militias, which command the loyalty of tens of thousands of fighters driving the conflict in Syria, have begun to consolidate their ranks. In late November, they announced they were banding together and forming the Islamic Front.
The more secular groups the U.S. has been backing have lost major ground to that group and the al Qaeda-linked forces, as well as to the Assad regime. Western diplomats estimate the new coalition accounts for about half of the rebels now fighting in the conflict.
The ascendancy of these militias spurred the Obama administration to authorize a senior U.S. envoy to meet with Islamist groups that aren't on State Department terrorist lists, according to a senior U.S. official.
The goal of the diplomacy, according to Western officials, is to persuade some Islamists to support a Syria peace conference in Geneva on Jan. 22, for fear that the talks won't yield a lasting accord without their backing. The outreach aims "to find out whether these people are worthwhile bringing into the diplomatic process," the U.S. official said.
More than two years into the civil war, the shift reveals the West's failure to unite Syria's fractious rebels under the banner of a secular opposition force capable of toppling the Assad regime. It is also a measure of how the West is scrambling to strengthen its hand ahead of the Geneva talks, where the regime is expected to arrive emboldened by military victories on the ground and staunch support from Russia and Iran.
Diplomats said they are trying to allay Islamist suspicions that the Geneva talks are a capitulation to the regime, which has agreed to attend while also publicly rejecting calls for Mr. Assad to relinquish power. However, there is a chance the regime will refuse to negotiate with Islamist groups that it regards as terrorists.
The goals of the Islamic Front militias contrast sharply with the agenda of key players attending the international peace talks who seek a secular framework for Syria's future government.
Throughout the civil war, the militias in the Islamic Front have been sandwiched between moderate rebel forces backed by the West and rebel groups affiliated with al Qaeda, at times juggling allegiances with both sides.
The critical difference between the two camps of Islamists is that al Qaeda's avowed enemies include not just Mr. Assad, but the West and its allies, including the Saudi monarchy. The Saudis and the U.S. fear those fighters could one day come from Syria to attack their governments, as happened after the Afghanistan and Iraq conflicts.
Saudi Arabia, the most ardent state opponent of Mr. Assad and his Iranian and Hezbollah allies, changed its strategy against the regime after spending nearly a half-billion dollars on arming the secular, American-backed rebel group. Saudi officials have said they are now fighting two wars in Syria: One against the regime, and the other against the growing ranks of al Qaeda-allied fighters flocking to the battlefield.
Bandar bin Sultan, the Saudi prince overseeing his country's support for the rebels, vowed to kill both Mr. Assad and extremists among the rebels in a conversation with a Western diplomat this fall, according to that official.
For most of the past two years, Saudi Arabia concentrated its support on the more secular, nationalist force of the Free Syrian Army, made up in part of army defectors. During that time, the kingdom spent $400 million on arms and equipment funneled to the force, according to the Western diplomat briefed by Saudis.
The U.S. and other allies joined the Saudis in training a small force of FSA rebels. But funding from other Arab Gulf states such as Qatar as well as from private Gulf patrons for Islamist rebels helped render the Saudi- and Western-backed secular opposition fighters virtually irrelevant, according to Saudi advisers, security analysts and rebels familiar with the situation.
Enlarge Image
Zahran Alloush, commander of the Army of Islam rebel group. Agence France-Presse/Getty Images
They said the Saudis are now pinning much of their hopes in Syria on a strengthening rebel force called Jaish al-Islam, or Army of Islam.
The group is part of the Islamic Front and its leader also commands the military arm of the Front.
One point of contention with the U.S. and Syrian activists is whether the Islamists the Saudis deem moderates really are. Saudi Arabia is a deeply religious and conservative country that follows one of the world's strictest interpretations of Islam.
The leader of Jaish al-Islam, Zahran Alloush, is a Syrian educated in Saudi Arabia whose father is a preacher in the Saudi holy city of Medina. Mr. Alloush pledged allegiance late last month to the Islamic Front.
On his purported Twitter feed and in interviews posted on YouTube, he has called for Syria to be ruled by an Islamic council rather than a democratically elected body. He also has spoken in YouTube videos approvingly of the torture of Shiite opponents fighting for Mr. Assad.
His rebel faction—with an efficient media arm that prominently features Mr. Alloush, usually in closely trimmed beard and tightfitting camouflage—denied it has taken funds from Saudi or any other Gulf state. However, Mr. Alloush has in tweets thanked private donors from the Gulf.
Jaish al-Islam is based in part in Ghouta, the Damascus suburb hit in August by the worst chemical attack of the civil war. At times, it coordinates with the al Qaeda-allied opposition forces on the battlefield, including in fighting this month to try to break regime sieges of Damascus suburbs.
Throughout the conflict, fractures among Syria's opposition forces have bedeviled the U.S. effort.
Western diplomats said they are pressing the Islamists to rein in their criticism of moderate leader Gen. Salim Idris and the Syrian National Council, the opposition's political umbrella group, arguing that tensions between the opposition factions risk undermining the Geneva peace conference.
Gen. Idris and Ahmad Jarba, head of the Istanbul-based SNC, have struggled to maintain discipline among their forces on the ground in Syria, Western diplomats said. And the umbrella group has no say over the activities of the Islamist militias.
A senior opposition official close to Gen. Idris said the general has welcomed the formation of the Islamic Front as a way to unify the opposition and exclude more extremist factions.
"The SNC and the Front talk on a regular basis on the ground," the opposition official said, adding that the "common denominator binding the two groups" is opposition to al Qaeda-linked rebels.
The official played down concerns that a more powerful Front will further diminish the clout of the moderate opposition. "It's not mutually exclusive," the official said.
The official also said the two major battalions in the Front will be the key to forming a spearhead for any future campaign to drive al Qaeda-linked ISIS out of northern and eastern Syria.
"It cannot be done without their buy-in. It's definitely understood by our Gulf partners. The question is do Western policy makers, specifically Washington, realize that the only way to fight back against al Qaeda is to work with these groups," the opposition official said.
The opening of contacts capped weeks of behind-the-scenes talks that had already begun to bolster the Islamists' diplomatic profile.
On Oct. 31, a group of militias that would eventually found the Islamic Front met with senior members of the FSA and the foreign minister of Qatar, a key military backer, for two days of talks in Istanbul, according to an opposition activist who attended the talks.
During the talks, the militias made a series of demands, according to the activist. First they asked for an overhaul of the Supreme Military Council, an umbrella group headed by Gen. Idris, saying its leaders weren't shipping enough arms to the Islamists.
The militias also demanded the SMC transfer its headquarters from Turkey to the front lines in Syria. Finally, the militias wanted to meet directly with envoys from the "London 11"—a diplomatic group that includes the U.S., the U.K., France, Saudi Arabia and other Gulf states.
At least one request was fulfilled: The meeting with the foreign diplomats.
A week later, Qatar arranged a meeting between the Islamists and envoys from the U.S., the U.K., France, Saudi Arabia, Turkey and other members of the London 11 on the outskirts of the Turkish capital Ankara, according to one Western diplomat. Senior members of Syria's most powerful Islamist militias, including Ahrar al-Sham, Suqoor al-Sham and the Tawheed Brigade, sat on the other side of the table, the diplomat said.
Qatar's Foreign Ministry didn't respond to a request for comment.
During the meeting, Western diplomats tried to heal the rift between the Islamists and Mr. Idris.
Diplomats with knowledge of the talks say they have reservations about some of the groups involved.
They cited allegations in a recent Human Rights Watch report that Ahrar al-Sham fought alongside Al Nusra in an Aug. 4 attack along Syria's Mediterranean coast that targeted children and women.
Ahrar al-Sham has denied the allegations, saying civilians who died in the clashes were either carrying weapons or fighting alongside the Assad regime.
Western diplomats said their engagement with the Islamists also aims to draw the powerful militias away from the Al Nusra Front and other groups affiliated with al Qaeda.
"We believe they are groups that, if we do nothing, may go toward more radicalization," one Western diplomat said.
—Rima Abushakra and Mohamad Nour Alakraa in Beirut and Cassell Bryan-Low in London contributed to this article.
Write to Stacy Meichtry at stacy.meichtry@wsj.com, Ellen Knickmeyer at ellen.knickmeyer@dowjones.com and Adam Entous at adam.entous@wsj.com