Here's how the latest US-led strikes unfolded

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

Here's how the latest strikes unfolded.

January 28: Three US service members were killed and dozens of others injured in a drone strike on their remote military outpost in Jordan, the Pentagon said. They were the first known US military fatalities from enemy 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 was launched by an Iran-backed militia from Iraq, and President Biden vowed to respond. The US has blamed Iranian-backed armed groups for launching more than 150 attacks since October on US troops stationed in the Middle East.

January 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 on Iran, but Mr. Biden's advisers said he was determined to avoid a broader regional conflict.

Friday: The United States carried out airstrikes on more than 85 targets in Syria and Iraq, targeting Iranian-backed forces, including the group it said was responsible for the attack in Jordan. The Pentagon said the attacks targeted command and control operations, intelligence centers, weapons facilities and bunkers used by the Islamic Revolutionary Guard Corps Quds Force and affiliated militias.

Afterwards, American officials said that Mr. Biden had not seriously considered attacking inside Iran, and that by attacking the facilities used by the powerful Quds Force, without trying to eliminate its leadership, the United States was trying indicating that they did not want all-out war.

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

Sunday: Shortly after the Houthis said they would respond to the U.S. and British attacks, U.S. forces said they had launched another attack on the group, destroying a cruise missile that “posed an immediate threat to U.S. naval and merchant ships in the region . ”