Saturday's strikes in Yemen followed ones in Iraq and Syria the day prior.
The United States on Friday began to carry out airstrikes against Iran-backed militants and Iranian military targets in Iraq and Syria in retaliation for a drone attack on an American base in Jordan on Jan. 28 that killed three U.S. service members.
Dozens of other American troops were wounded in the drone attack on the Tower 22 base near Jordan's border with Iraq and Syria. The U.S. says Iran is responsible for funding and arming the militants while Iran has denied involvement.
U.S. President Joe Biden had quickly warned that America would respond forcefully, escalating U.S. involvement in the Middle East after months of trying to contain tensions from boiling over into a broader war in the region.
The U.S. has attributed the drone attack on the American base in Jordan to the Islamic Resistance in Iraq, an umbrella group of Iran-backed militias.
According to a U.S. official, the drone that successfully hit the base was an Iranian-made Shahed drone, similar to those used by the Russians on the battlefield in Ukraine.
Iran has denied involvement in the Jordan strike. But President Joe Biden earlier this week faulted Iran for providing munitions and funding to these different proxy groups.
The U.S. base is known as Tower 22, a major logistical hub for U.S. troops still in Syria on a mission to prevent a resurgence by Islamic State fighters. According to Central Command, there are approximately 350 U.S. Army and Air Force personnel deployed to the base.
Retaliatory U.S. airstrikes have begun in Syria and Iraq, U.S. officials say.
-ABC News' Luis Martinez
US begins retaliatory military strikes in Syria and Iraq
An initial battery of strikes in Syria did not come from the U.S., sources say. U.S. strikes are still anticipated.
Secretary of State Antony Blinken will travel to the Middle East from Sunday to Thursday, making stops in Saudi Arabia, Egypt, Qatar, Israel, and the West Bank.
It will mark Blinken’s fifth visit to the region since Oct. 7.
One focus, according to the State Department, will be to continue work to prevent the conflict from spreading -- a major concern as the U.S. readies retaliatory strikes -- while also “reaffirming that the United States will take appropriate steps to defend its personnel and the right to freedom of navigation in the Red Sea.”
Biden joined grieving families at Dover Air Force Base in Delaware to witness the return of the remains of three fallen Army reservists killed in Jordan.
He was accompanied by first lady Jill Biden, Defense Secretary Lloyd Austin and Joint Chiefs Chairman Gen. CQ Brown.
They met with the families privately before receiving the remains, the White House said.
The Pentagon identified the fallen soldiers as Sgt. William Jerome Rivers, 46, of Carrollton, Georgia.; Spc. Kennedy Ladon Sanders, 24, of Waycross, Georgia.; and Spc. Breonna Alexsondria Moffett, 23, of Savannah, Georgia.
