WASHINGTON – Al-Qaida has advanced beyond isolated pockets of activity in Syria and now 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 Iraq-like foothold that would be hard to defeat if rebels eventually oust President Bashar Assad.

At least a couple of hundred al-Qaida-linked militants are operating in Syria, and their ranks are growing as foreign fighters stream into the Arab country daily, current and former U.S. intelligence officials said.

The units are spreading from city to city, with veterans of the Iraq insurgency employing their expertise in bomb-building to carry out more than two dozen attacks so far. Others are using their experience in coordinating small units of fighters in Afghanistan to win new followers.