U.S. President Joe Biden has said he will revenge an attack by Iran-backed militant groups that killed 3 Americans and injured over 30 others in Jordan.

According to Biden, the incident 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 that at least 34 personnel were being evaluated for traumatic brain injuries.

“And we shall respond,” he added.

Amid a heightened risk of escalation in the region, shaken by the war in Gaza, U.S. officials have assessed that one of several Iranian-backed groups was responsible for the attack on the U.S. soldiers, but still had to identify the precise group responsible.

“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 in the statement.

Jordan condemned what it called a “terrorist attack” on a military site, saying it was cooperating with the United States to fortify its border defences.

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.

Jordan is a close ally of the United States in the Middle East, with the Pentagon basing some 3,000 troops

Iran on Monday denied that it had any links to the attack, with the Foreign Ministry in Tehran calling the accusations “baseless.”

Foreign Ministry spokesperson Nasser Kanaani said “resistance groups” in the region do not take orders from Tehran.

Earlier, Iran’s diplomatic mission to the United States, through its Permanent Mission to the United Nations, said “Iran had no connection and had nothing to do with the attack on the U.S. base.”

Military analysts say the attack is sure to increase pressure on the Biden administration to take firm action.