Residents gather around destroyed buildings after US warplanes carried out an airstrike on the headquarters of Hashd al-Shaabi in Al-Qaim city of Anbar, Iraq on February 3.
CNN  — 

The United States on Friday conducted major airstrikes on dozens of targets across Iraq and Syria in retaliation for a drone attack in Jordan last month that killed three US troops.

The strikes were larger in number and scale than previous ones launched since October, when Iran-backed armed groups began attacking US forces across the region in protest of Israel’s war in Gaza.

With the US warning of more strikes to follow, here’s what we know.

What triggered the strikes?

The US strikes were in response to a drone attack by Iran-backed militants on a US military outpost in Jordan on January 28, which killed three US service members and wounded more than 40 others.

The attack marked the worst loss of US military life in the region in nearly three years and the first US military fatalities since the war in Gaza erupted.

US President Joe Biden at the time vowed to hold “all those responsible to account at a time and in a manner our choosing.”

The attack in Jordan marked a significant escalation in tensions between the US and Iran-backed groups attacking American bases across the region in protest at Israel’s war in Gaza. Believed to be funded and trained by Iran, these groups view the US as responsible for Israel’s actions by supplying weapons to the Jewish state and failing to force a ceasefire.

Immediately after US officials in Washington received word that Tower 22 in Jordan was struck, Biden was presented with, and approved, a range of options on Sunday for retaliation, multiple sources told CNN.

Biden specifically gave the green light for the first set of strikes in Iraq and Syria that was executed Friday in a Situation Room meeting with his top national security advisers on Monday.

It was in that same meeting that the president was informed with the assessment that Islamic Revolutionary Guard Corps-backed militant groups were to blame for the Sunday drone attack, according to the sources.

Since October, when the Israel-Hamas war began, the US military has carried out several strikes targeti