U.S. President Joe Biden said three U.S. service members were killed and "many" wounded in a drone attack on U.S. forces stationed in northeastern Jordan near the Syrian border.
"While we are still gathering the facts of this attack, we know it was carried out by radical Iran-backed militant groups operating in Syria and Iraq," Biden said in a statement.
"We will carry on their commitment to fight terrorism. And have no doubt -- we will hold all those responsible to account at a time and in a manner of our choosing," Biden said on January 28.
U.S. President Joe Biden
Biden said the attack took place late on January 27. He did not specify the number of those injured in the incident, but a U.S. official later said at least 34 personnel were being evaluated for traumatic brain injuries.
Jordan condemned what it called a "terrorist attack" on a military site, saying it was cooperating with the United States to fortify its border defenses.
Earlier, a government spokesman in Amman claimed the attack was not on Jordanian soil but on a U.S. base in Syria just across the border.
The details of the attack could not immediately be verified, but reports said it occurred at Tower 22, a site hosting a contingent of U.S. troops inside Jordan along the Syria border.
Gregory Brew, a historian and analyst with the geopolitical risk firm Eurasia Group, told RFE/RL’s Radio Farda that the attack represented a "major escalation -- and the U.S. is bound to respond forcefully and promptly."
"The response is likely to come through more intense U.S. action against Iran-backed militias in either Syria and Iraq. It's unclear if this was an intentional escalation by Iran and its allies, but the genie is out of the bottle," he added.
Karim Sajadpour of the Washington-based Carnegie Endowment for International Peace told Radio Farda that "U.S. deterrence against Iran is clearly not working."
"Iran and its proxies are killing U.S. soldiers and publicly taking credit for it. If they feared the consequences they would not be so brazen," he added.
Republican Senator Tom Cotton, a vocal critic of Biden, said the "only answer to these attacks must be devastating military retaliation against Iran's terrorist forces.... Anything less will confirm Joe Biden as a coward."
Jordan is a close ally of the United States in the Middle East, with the Pentagon basing some 3,000 troops there, often in support of actions in Syria.
U.S. troops have been active in Syrian in recent years battling the Islamic State (IS) extremist group and others.
If confirmed to be in Jordan, the attack would be first targeting U.S. troops in that country since the start of Israel's war in Gaza with Hamas, which has been declared a terrorist organization by Washington and the European Union.
SEE ALSO: U.S. And Iran-Backed Huthis Engaged In High-Stakes Fight Tehran Wants To AvoidMany observers have expressed fears of a widening conflict in the Middle East after war broke out in Gaza following Hamas's attack on Israel on October 7.
At least 1,200 people were killed in those assaults, leading to retaliatory Israeli actions that have killed more than 26,000 Palestinians, according to local officials.
Because of its support for Israel, U.S. forces have been the target of Islamist groups in the Middle East, including Iranian-backed Huthi rebels based in Yemen and militia groups in Iraq who are also supported by Tehran.