WASHINGTON -- Al-Qaeda has moved beyond isolated pockets of activity in Syria and is building a network of well-organized cells, according to U.S. intelligence officials who fear the terrorists could be on the verge of establishing an Iraqlike foothold that would be hard to defeat if rebels eventually oust Syrian President Bashar Assad.
At least a couple of hundred al-Qaeda-linked militants operate in Syria and their ranks are growing as foreign fighters stream into the Arab country daily, current and former U.S. intelligence officials say.
The units are spreading from city to city, with veterans of the Iraq insurgency employing expertise in bomb-building to carry out more than two dozen attacks so far.
Others are using experience in coordinating small units of fighters in Afghanistan to win followers.
In Syria on Friday, rebel commanders appealed for new and better weapons from abroad, complaining Mr. Assad's forces have them outgunned from the air and on the ground.
Rebel leaders say with so little aid from the United States and other nations, they are losing the battle for influence against hard-line militants. They say their fighters are sometimes siding with extremists who are better funded and armed so they can fight the stronger Syrian army.
It could point to a widening danger posed by extremists who have joined rebels to fight the Assad government.
The intelligence offers some rationale for White House reluctance to give military aid to the insurgency, which Washington says it is trying to better understand. U.S. officials have repeatedly rejected providing lethal assistance to the conflict that has killed at least 19,000 people over 17 months.
With the U.S. government weighing options, Secretary of State Hillary Clinton will meet with Turkish officials and Syrian opposition activists in Istanbul today.
Officials described the intelligence situation on condition of anonymity.
Underscoring the administration's desire to step up efforts against the Assad government without providing weapons, the United States set largely symbolic sanctions Friday on Syria's state-run oil company and Iranian-backed Hezbollah.
It accused Iran and the Lebanese Shiite militant group of helping prop up Assad.
Neither action means much immediately. Americans have been barred from doing business with Hezbollah since the United States declared it a terrorist group in the 1990s.
Meanwhile, Syrian rebels were low on ammunition and guns and appealed for global help as government forces tried to consolidate control over Aleppo, the country's largest city and a deadly battleground in recent weeks.
In Aleppo Friday, government forces backed by jets, helicopters, artillery, and tanks reportedly resumed pursuit of rebels, who claimed to be counterattacking in cat-and-mouse fighting after pulling back from the most contested area of the city.
The surge in violence in recent days sent tens of thousands of Syrians fleeing to neighboring Lebanon, Turkey, Jordan, and Iraq.
In those countries, the U.N. refugee agency said Friday, a total of more than 146,000 Syrians had registered as refugees, or were in the process of registering, since the fighting began.
In other developments, fighting broke out between Jordanian and Syrian forces in a border region between the two countries overnight, but a Jordanian source said today no one on Jordan's side appeared to have been killed.
A Syrian opposition activist who witnessed the fighting said armored vehicles were involved in the clash in the Tel Shihab-Turra area, about 50 miles north of the Jordanian capital, Amman, that occurred after Syrian refugees tried to cross into Jordan.
Jordanian troops have fired near the border in the past to stop Syrians from shooting at fleeing refugees.