A US official, in confirming the raid, said the attack targeted elements of a robust foreign fighter logistics network and that due to Syrian inaction the US was now "taking matters into our own hands."

"We still have a certain level of foreign fighter movement, not much, through Anbar, because of our activities out there," Kelly said. But he said Iraqi intelligence believes al Qaeda operatives and others "live pretty openly on the Syrian side, and periodically we know that they try to come across."

The flow of foreign fighters into Iraq has been cut to an estimated 20 a month, a senior U.S. military intelligence official told the Associated Press in July. That's a 50 percent decline from six months ago, and just a fifth of the estimated 100 foreign fighters who were infiltrating Iraq a year ago, according to the official, speaking on condition of anonymity in order to discuss intelligence reports.

Ninety percent of the foreign fighters enter through Syria, according to U.S. intelligence. Foreigners are some of the most deadly fighters in Iraq, trained in bomb-making and with small-arms expertise and more likely to be willing suicide bombers than Iraqis.

Foreign fighters toting cash have been al-Qaida in Iraq's chief source of income. They contributed more than 70 percent of operating budgets in one sector in Iraq, according to documents captured in September 2007 on the Syrian border. Most of the fighters were conveyed through professional smuggling networks, according to the report.

The U.S. military official said that while American forces have had considerable success, with Iraqi help, in shutting down the "rat lines" in Iraq, and with foreign government help in North Africa, the Syrian node has been out of reach.