BY ZEKE MILLER (AP White House Correspondent)

COLUMBIA, S.C. (AP) — Three American troops were killed and “many” were wounded Sunday in a drone strike in northeast Jordan near the Syrian border, President Joe Biden said. He blamed Iran-backed militias for the first U.S. fatalities after months of strikes by the groups against American forces across the Middle East amid the Israel-Hamas war.

With an increasing the risk of military escalation in the region, U.S. officials were working to conclusively identify the precise group responsible for the attack, but they have assessed that one of several Iranian-backed groups was behind it.

Biden said the United States “will hold all those responsible to account at a time and in a manner (of) our choosing.”

According to a U.S. official, at least 25 U.S. service members were wounded, but that number may grow. The official, who spoke on condition of anonymity to discuss details not made public, said a large drone struck the base, which is in Jordan, right on the Syrian border. It is used largely by troops involved in the advise-and-assist mission for Jordanian forces. The small installation includes U.S. engineering, aviation, logistics and security troops.

Jordanian state television quoted Muhannad Mubaidin, a government spokesman, as insisting the attack happened outside of the kingdom across the border in Syria. U.S. officials insisted that the attack took place in Jordan.

U.S. troops long have used Jordan, a kingdom bordering Iraq, Israel, the Palestinian territory of the West Bank, Saudi Arabia and Syria, as a basing point. U.S. Central Command said 25 service members were injured the attack in addition to the three killed.

Some 3,000 American troops typically are stationed in Jordan.

Two U.S. officials said the attack occurred at the base in northeastern Jordan known as Tower 22. Previously released U.S. military photos in 2018 identify troops working at the base as supporting special operation forces in the area, likely across the border into Syria. The U.S. military base at al-Tanf in Syria is just some 20 kilometers (12 miles) north of Tower 22. The installation provide a critical logistical hub for U.S. forces in Syria, including those at al-Tanf, which is near the intersection of the Iraq, Syria and Jordan borders.

Since Israel’s war on Hamas in the Gaza Strip began, U.S. troops in Iraq and Syria have faced drone and missile attacks on their bases. The attack on Jordan marks the first targeting American troops in Jordan during the war and the first to result in the loss of American lives. Other attacks have left troops seriously injured, including with traumatic brain injuries.

The U.S. in recent months has struck targets in Iraq, Syria and Yemen to respond to attacks on American forces in the region and to deter Iranian-backed Houthi rebels from continuing to threaten commercial shipping in the Red Sea.

Biden, who was in Columbia, South Carolina, on Sunday, was briefed by Defense Secretary Lloyd Austin, national security adviser Jake Sullivan, and principal deputy national security adviser Jon Finer, White House press secretary Karine Jean-Pierre said. He was expected to meet again with his national security team later Sunday.

The president called it a “despicable and wholly unjust attack” and said the service members were “risking their own safety for the safety of their fellow Americans, and our allies and partners with whom we stand in the fight against terrorism. It is a fight we will not cease.”

Syria is still in the midst of a civil war and long has been a launch pad for Iranian-backed forces there, including the Lebanese militia Hezbollah. Iraq has multiple Iranian-backed Shiite militias operating there as well.

Jordan, a staunch Western ally and a crucial power in Jerusalem for its oversight of holy sites there, is suspected of launching airstrikes in Syria to disrupt drug smugglers, including one that killed nine people earlier this month.

An umbrella group for Iran-backed factions known as the Islamic Resistance in Iraq earlier claimed launching explosive drone attacks targeting three areas in Syria, as well as one inside of “occupied Palestine.” The group has claimed responsibility for dozens of attacks against bases housing U.S. troops in Iraq and Syria since the Israel-Hamas war began.

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Associated Press writers Bassem Mroue in Beirut, Omar Akour in Amman, Jordan, Jon Gambrell in Jerusalem and Lolita C. Baldor in Washington contributed to this report.