DAMASCUS, Syria (AP) — U.S. military helicopters launched an extremely rare attack Sunday on Syrian territory close to the border with Iraq, killing eight people in a strike the government in Damascus condemned as “serious aggression.”

A U.S. military official said the raid by special forces targeted the network of al-Qaida-linked foreign fighters moving through Syria into Iraq. The Americans have been unable to shut the network down in the area struck because Syria was out of the military’s reach.

The attack came just days after the commander of U.S. forces in western Iraq said American troops were redoubling efforts to secure the Syrian border, which he called an “uncontrolled” gateway for fighters entering Iraq.