WASHINGTON (AP) — The Pentagon says the U.S. has launched an airstrike on a site in eastern Syria.

It targeted a facility linked to Iranian-backed militias, in retaliation for what has been a growing number of attacks on bases housing U.S. troops in the region for the past several weeks.

The strike by two U.S. F-15 fighter jets was on a weapons storage facility linked to Iran’s Revolutionary Guard.

This is the second time in less than two weeks that the U.S. has bombed facilities used by the militant groups, many operating under the umbrella of the Islamic Resistance in Iraq.

U.S. officials say the militants have carried out at least 40 such attacks since Oct. 17.