U.S. Strikes in Yemen, Syria and Iraq: A Timeline

The United States has led a major wave of retaliatory strikes in the Middle East, hitting scores of targets belonging to Iranian-backed armed groups since Friday. The strikes are a sharp escalation of hostilities in the region, one that President Biden had sought to avoid since the war between Israel and Hamas in Gaza began in October.

Here is how the latest strikes have unfolded.

Jan. 28: Three U.S. service members were killed and dozens of others were injured in a drone attack on their remote military outpost in Jordan, the Pentagon said. They were the first known American military fatalities from hostile fire in the Middle East since October, when regional tensions rose with the start of Israel’s war against Hamas in Gaza.

The Biden administration said the drone had been launched by an Iran-backed militia from Iraq, and President Biden pledged to respond. The U.S. has blamed Iranian-backed armed groups for launching more than 150 attacks since October on U.S. troops stationed in the Middle East.

Jan. 30: President Biden said he had decided on a response to the attack in Jordan, but did not say what it would be. Some Republican lawmakers called for a direct strike against Iran, but Mr. Biden’s advisers said he was determined to avoid a wider regional conflict.

Friday: The United States carried out airstrikes on more than 85 targets in Syria and Iraq, aiming at Iranian-backed forces including the group it said was responsible for the Jordan strike. The Pentagon said the strikes targeted command and control operations, intelligence centers, weapons facilities and bunkers used by Iran’s Islamic Revolutionary Guards Corps Quds Force and affiliated militia groups.

Afterward, U.S. officials said that Mr. Biden had not seriously considered striking inside Iran, and that by targeting facilities used by the powerful Quds Force, while not attempting to take out its leadership, the United States sought to signal that it did not want all-out war.

Saturday: American and British warplanes, with support from six allies, launched strikes at dozens of sites in Yemen controlled by Houthi militants. A joint statement from the allies said that the targets included weapons storage facilities, missile launchers, air defense systems and radars, and that the strikes were intended to deter the Houthis’ attacks on Red Sea shipping.

Sunday: Shortly after the Houthis said they would respond to the U.S. and British strikes, American forces said they had carried out another attack on the group, destroying a cruise missile that had posed “an imminent threat to U.S. Navy ships and merchant vessels in the region.”