Iraqi security sources said after a lull of several months Al Qaida has increased the flow of insurgents from Syria to Iraq. In late November, the sources said, more than 150 recruits arrived in Iraq to join Al Qaida in such provinces as Anbar and Diyala.

"The Al Qaida network issued an urgent appeal for more fighters because of our successes against the terrorists," a security source said.

The Al Qaida drive was expected, the sources said. They said Iraqi security forces found a letter from Al Qaida network chief Abu Hamza Al Muhajir that called on supporters throughout the Middle East to send fighters immediately.

In November 2007, the U.S.-led coalition and Iraqi security forces killed or captured 40 senior Al Qaida operatives, the U.S. military said. On Tuesday, U.S. military spokesman Maj. Gen. Kevin Bergner said the targets included senior commanders, improvised-explosive-device cell leaders, foreign facilitators, and facilitators of logistics, communications and finances for insurgency networks.

"As security improves, Iraqi citizens continue to step forward to work with Iraqi and coalition forces to reduce the violence in Iraq," Bergner said.

Many of the new Al Qaida recruits have joined units in Anbar, Diyala, Kirkuk, Mosul and Salah Eddin. The sources said this could result in a resurgence in suicide bombings and other attacks over the next few weeks.

Iraq and the United States have provided incentives for Muslims to identify Al Qaida inmates. Officials said the so-called moderate Muslims have pointed out thousands of Al Qaida members or sympathizers, who were then placed in separate cells.

"What we had were moderates who said, 'Listen, you know, we don't want that [extremist] direction,'" U.S. Marine Maj. Gen. Douglas Stone said on Tuesday. "The moderates will turn in the extremists. Now that we can physically do that, almost every day groups of 50 to 100 to 150 to 200 [detainees] will self-identify the guys, will pull them out."