The strikes, which included the use of long-range B-1 bombers flown from the United States, were the first in response to the attack last weekend in Jordan by Iran-backed militants, and more US military operations are expected in the coming days.
The strikes intensified a conflict that has spread into the region since war erupted between Israel and Hamas after the Palestinian group's deadly assault on Israel on Oct.7.
Iran's foreign ministry spokesperson Nasser Kanaani said in a statement the attacks represented "another adventurous and strategic mistake by the United States that will result only in increased tension and instability".
Iraq summoned the US charge d'affaires in Baghdad to deliver a formal protest. Iraq's Popular Mobilization Forces, a state security force including Iran-backed groups, said 16 of its members were killed including fighters and medics. The government earlier said civilians were among 16 dead.
In Syria, the strikes killed 23 people who had been guarding the targeted locations, said Rami Abdulrahman, director of the Syrian Observatory for Human Rights, which reports on war in Syria.
US Lieutenant General Douglas Sims, the director of the Joint Staff, said the attacks appeared to be successful, triggering large secondary explosions as the bombs hit militant weaponry. He said the strikes were undertaken knowing that there would likely be casualties among those in the facilities.
Despite the strikes, the Pentagon has said it does not want war with Iran and does not believe Tehran wants war either, even as Republican pressure has increased on US President Joe Biden to deal a blow directly.
Iran, which backs Hamas, has sought to stay out of the regional conflict itself even as it backs groups that have entered the fray from Lebanon, Yemen, Iraq and Syria - the so-called "Axis of Resistance" that is hostile to Israel and US interests.
US Defense Secretary Lloyd Austin said after the strikes that Biden had directed additional action against the IRGC and those linked to it. "This is the start of our response," Austin said.
"We do not seek conflict in the Middle East or anywhere else, but the president and I will not tolerate attacks on American forces," Austin said.
An Iraqi government statement said the areas bombed by US aircraft included places where Iraqi security forces are stationed near civilian locations. It said 23 people had been wounded in addition to the 16 killed.
The White House said the United States had informed Iraq ahead of strikes. Baghdad later accused the United States of deception, saying a US claim of coordination with the Iraqi authorities was "unfounded".
On Friday, Iran's President Ebrahim Raisi said his country will not start a war, but it will "respond strongly" to anyone who bullies it. He did not mention the US strikes in a speech on Saturday marking Iran's space technology day.
Iran's ambassador in Damascus Hossein Akbari, in comments reported by the semi-official Fars news agency, played down the airstrikes, denying Iran-linked targets were hit and saying the aim was "to destroy Syria's civil infrastructure".
Hamas said Washington was pouring "oil on the fire".Britain called the United States its "steadfast" ally and said it supports Washington's right to respond to attacks.
Polish Foreign Minister Radek Sikorski, arriving for an EU meeting in Brussels, said the US strikes were the result of Iranian proxies "playing with fire".
The strikes hit targets including command and control centres, rockets, missiles and drone storage facilities, as well as logistics and munition supply chain facilities, the US military said.
In Iraq, residents said several strikes hit the Sikak Neighborhood in Al-Qaim, a residential area that locals said was also used by armed groups to store large amounts of weapons. Militants had left the area and gone into hiding in the days since the Jordan attack, local sources said.
Khaled Walid, a Sikak resident, said that the US strikes and secondary explosions of munitions stored in the neighborhood had caused widespread damage.
US troops have been attacked over 160 times in Iraq, Syria and Jordan since Oct. 7, usually with a mix of rockets and one-way attack drones, prompting the United States to mount several retaliatory attacks even before the latest strikes.
US President Joe Biden attends the dignified transfer of the remains of Army Reserve Sergeants William Rivers, Kennedy Sanders and Breonna Moffett, three US service members who were killed in Jordan during a drone attack. PHOTO: Reuters
The United States has assessed that the drone that killed the three soldiers and wounded more than 40 other people in Jordan was made by Iran, US officials have told Reuters.
"Our response began today. It will continue at times and places of our choosing," Biden said.
The top Republican on the Senate Armed Services Committee, Roger Wicker, criticised Biden for failing to impose a high enough cost on Iran, and taking too long to respond.
Iranian advisers assist armed groups in both Iraq, where the United States has around 2,500 troops, and Syria, where it has 900.
The United States launched the air strikes against Iran-backed groups in Iraq and Syria in retaliation for a recent drone attack on an American base in Jordan that killed three US soldiers.
Syria’s culture ministry condemned “in the strongest terms the barbaric US bombardment of the Al-Rahba fortress” in eastern Syria’s Mayadeen area.
In a statement on social media, it said the citadel, located along the Euphrates River, dates to the ninth century, without elaborating on the damage the site sustained.
The “blatant” attack violated “all international norms and charters that call for the protection and respect for cultural property,” the ministry added.
Pro-government daily Al-Watan reported antiquities chief Nazir Awad as saying the bombardment late Friday caused cracks and fissures in the fortress walls.
The full extent of the damage had not yet been assessed, Al-Watan cited Awad as saying.
Damascus said earlier Saturday that the overnight strikes killed “a number of civilians and soldiers, wounded others and caused significant damage to public and private property.”
With tensions in the Middle East already running high over the Israel-Hamas war in Gaza, Damascus, Baghdad and Tehran on Saturday accused Washington of undermining the stability of the region.
