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

The massive barrage of strikes hit more than 85 targets at seven locations, including command and control headquarters, intelligence centres, 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 with and arming of regional militias. President Joe Biden made it clear in a statement that there would be more to come.

The US strikes appeared to stop short of directly targeting Iran or senior leaders of the Revolutionary Guard Quds Force within its borders, as the US tries to prevent the conflict from escalating further. Iran has denied it was behind the Jordan attack.

It was unclear what the impact will be of the strikes. Days of US warnings may have sent militia members scattering into hiding. With groups operating at locations in several countries, a knockout blow is unlikely.

Though one of the main Iran-backed militias, Kataib Hezbollah, said it was suspending attacks on American troops, others have vowed to continue fighting, casting themselves as champions of the Palestinian cause while the war in Gaza shows no sign of ending.

‘‘Our response began today. It will continue at times and places of our choosing,’’ Biden warned.

‘‘Let all those who might seek to do us harm know this: If you harm an American, we will respond.’’

He and other top US leaders had been saying for days that any American response wouldn’t be just one hit but a ‘‘tiered response’’ over time. National Security Council spokesman John Kirby said the targets ‘‘were carefully selected to avoid civilian casualties and based on clear, irrefutable evidence that they were connected to attacks on US personnel in the region.’’

He declined to detail what that evidence was.

The strikes took place over about 30 minutes, and three of the sites struck were in Iraq and four were in Syria.

US Central Command said the assault involved more than 125 precision munitions, and they were delivered by numerous aircraft, including long-range B-1 bombers flown from the United States.

It’s not clear, however, whether militia members were killed.

Syrian state media reported that there were casualties but did not give a number. The UK-based Syrian Observatory for Human Rights reported that 18 militants were killed in the Syria strikes.

The assault came just hours after Biden and top defence leaders joined grieving families to watch as the remains of the three Army Reserve soldiers were returned to the US at Dover Air Force Base in Delaware.

The US has blamed the Islamic Resistance in Iraq, a broad coalition of Iran-backed militias, for the attack in Jordan, but hasn’t narrowed it down to a specific group.