Updated Friday, Nov. 14, 2014 at 9:06 p.m. ET with comment from Director of National Intelligence James Clapper.
ISTANBUL -- Militant leaders from the Islamic State of Iraq and Syria (ISIS) and al Qaeda gathered at a farm house in northern Syria last week and agreed on a plan to stop fighting each other and work together against their opponents, a high-level Syrian opposition official and a rebel commander have told The Associated Press.
Such an accord could present new difficulties for Washington's strategy against ISIS. While warplanes from a U.S.-led coalition strike militants from the air, the Obama administration has counted on arming "moderate" rebel factions to push them back on the ground. Those rebels, already considered relatively weak and disorganized, would face far stronger opposition if the two heavy-hitting militant groups now are working together.
ISIS - the group that has seized nearly a third of Syria and Iraq with a campaign of brutality and beheadings this year - and al Qaeda's affiliate in Syria, known as the Nusra Front, have fought each other bitterly for more than a year to dominate the rebellion against Syrian President Bashar Assad.
The Associated Press reported late last month on signs that the two groups appear to have curtailed their feud with informal local truces. Their new agreement, according to the sources in rebel groups opposed to both ISIS and Nusra Front, would involve a promise to stop fighting and team up in attacks in some areas of northern Syria.
Cooperation, however, would fall short of unifying the rival groups, and experts believe any pact between the two sides could easily unravel. U.S. intelligence officials have been watching the groups closely and say a full merger is not expected soon - if ever. In an interview with "Face the Nation" moderator Bob Schieffer, Director of National Intelligence James Clapper said Friday: "There have been tactical accommodations on the battlefield, on occasion, where local groups have united in the interest of a tactical objective, but broadly, I don't see those two uniting, at least yet."
On Thursday, U.S. Defense Secretary Chcuk Hagel said the military remains "sober" about the challenges of fighting ISIS in the midst of Syria's raging civil war.
The mission to train and equip moderate Syrian rebels, which was approved by Congress in September, will not begin to make a difference on the ground for another eight to 12 months, he said.
According to a Syrian opposition official speaking in Turkey, the meeting took place Nov. 2 in the town of Atareb, west of Aleppo, starting at around midnight and lasting until 4 a.m. The official said the meeting was closely followed by members of his movement, and he is certain that an agreement was reached. The official said about seven top militant leaders attended.
A second source, a commander of brigades affiliated with the Western-backed Free Syrian Army who is known as Abu Musafer said he also had learned that high-ranking members of Nusra and IS met on Nov. 2. He did not disclose the exact location, but said it was organized by a third party and took place in an area where the FSA is active.
According to Abu Musafer, two decisions were reached: First, to halt infighting between Nusra and ISIS and second, for the groups together to open up fronts against Kurdish fighters in a couple of new areas of northern Syria.
The Nusra Front has long been seen as one of the toughest factions trying to oust Assad in a civil war estimated to have killed more than 200,000 since 2011. ISIS entered the Syria war in 2012 from its original home in Iraq and quickly earned a reputation for brutality and for trying to impose itself as the leading faction in the rebellion behind which all pious Muslims should united. Al Qaeda initially rejected ISIS's claims to any role in Syria, and Nusra and other factions entered a war-within-a-war against it. But ISIS swelled in power and became flush with weapons and cash after overrunning much of northern and western Iraq over the summer.
According to the opposition official, the meeting included an ISIS representative, two emissaries from Nusra Front, and attendees from the Khorasan Group, a small but battle-hardened band of al Qaeda veterans from Afghanistan and Pakistan. Also reported present at the meeting was Jund al-Aqsa, a hard-line faction that has sworn allegiance to ISIS; and Ahrar al-Sham, a conservative Muslim rebel group.
The official said ISIS and the Nusra Front agreed to work to destroy the Syrian Revolutionaries Front, a prominent rebel faction armed and trained by the United States and led by a fighter named Jamal Maarouf. They agreed to keep fighting until all of the force, estimated to be 10,000 to 12,000 fighters, was eliminated, the official said.
During the meeting, ISIS also offered to send extra fighters to Nusra Front for an assault it launched last week on Western-backed rebels from the Hazm Movement near the town of Khan al-Sunbul in northern Syria, the official said. ISIS sent about 100 fighters in 22 pickup trucks but Nusra ended up not needing the assistance, he said, because Hazm decided not to engage in the fight. Sixty-five Hazm fighters defected to Nusra, he said.
Tom Joscelyn, an American analyst who tracks terror groups for the website Long War Journal, said he hasn't seen any messaging that would confirm that the two groups have formally joined forces on the battlefield. But he said there has been information emerging before the reported Nov. 2 meeting "that would seem to fit in with that being what they were driving at. There has been a big push on the al Qaeda side to get this (alliance) through."
If they work together, the jihadis will be more effective in Syria, he said. "If there is less blood being spilled against each other and they don't have to worry about that, that's going to make it easier for the jihadis to go after Assad or any western-backed forces."