The U.S. military launched an air assault on dozens of sites in Iraq and Syria used by Iranian-backed militias and the Iranian Revolutionary Guard Friday, in the opening salvo of retaliation for the drone strike that killed three U.S. troops in Jordan last weekend, according the the U.S. military and officials.

President Joe Biden and other top U.S. leaders had been warning for days that America would strike back at the militias, and they made it clear it wouldn’t be just one hit but a “tiered response” over time.

“This afternoon, at my direction, U.S. military forces struck targets at facilities in Iraq and Syria that the IRGC and affiliated militia use to attack U.S. forces,” Biden said in a statement. “Our response began today. It will continue at times and places of our choosing.”

The massive barrage of strikes by manned and unmanned aircraft hit more than 85 targets at seven locations, including command and control headquarters, intelligence centers, rockets and missiles, drone and ammunition storage sites and other facilities that were connected to the militias or the IRGC’s Quds Force, the Guard’s expeditionary unit that handles Tehran’s relationship and arming of regional militias.

U.S. Central Command said the strikes used more than 125 precision munitions, and they were delivered by numerous aircraft, including long-range bombers flown from the United States. One official, who spoke on condition of anonymity to discuss details of the operation, said B-1 bombers were used.