Syria and Iraq say civilians were among those killed in the attacks.

The aftermath of US military strikes on locations in Syria and Iraq came into focus on Saturday morning when a Britain-based Syria monitoring group said at least 18 members of an Iran-backed group had been killed in attacks there and the Iraqi government said that 16 people had been killed, including civilians.

The Biden administration warned that the overnight attacks on locations used by Iranian forces and Iranian-backed militias in retaliation for the killing of three US troops last week would not be the last.

Both civilians and soldiers were among those killed in Syria, the country's defense ministry said. At least 18 members of Iranian-backed groups were killed in attacks on 26 locations there, according to the Syrian Observatory for Human Rights, a Britain-based monitoring group that has researchers in Syria.

The Iraqi government said in a statement on Saturday that the attacks had killed 16 people, including civilians, and injured another 25.

U.S. officials said they were confident the strikes on 85 targets in seven locations in the two countries had hit “exactly what they wanted to hit,” but said analysts would make a further assessment in daylight.

U.S. officials also said the targets were all linked to specific attacks on U.S. forces in the region, describing them as command and control operations, intelligence centers, weapons facilities and bunkers used by the Islamic Revolutionary Guard Corps' Quds Force and affiliated militia groups.

“Our response began today,” President Biden said in a statement shortly after witnessing the return of the bodies of the US soldiers killed at a military outpost in Jordan last week.

Friday's attacks hit no targets in Iran. Both Washington and Tehran have made it clear in recent days that they do not want direct conflict.

Brig. General Yahya Rasool, a spokesman for the Iraqi military, released a statement calling the attacks on Iraq “unacceptable” and a violation of the country's sovereignty, warning that the escalation “will drag down Iraq and the region with unforeseen consequences .” John F. Kirby, a spokesman for the U.S. National Security Council, said the Iraqi government had been notified before the attacks.

More than 125 precision munitions were used in the attacks, according to a statement from the United States Central Command. The attacks lasted 30 minutes, officials said, and were carried out largely by two U.S. B-1B bombers, which took off from Dyess Air Force Base in Texas early Friday on a flight of more than 6,000 miles. Using U.S.-based bombers allowed commanders in the region to keep their land and aircraft carriers in reserve for follow-on attacks, an official said.

Since the start of the war between Israel and Hamas on October 7, which has devastated Gaza and set the Middle East ablaze, Iran and its allied militias have carried out more than 160 attacks on US forces in the region and commercial ships attacked in the Red Sea. .