WASHINGTON

US Defense Secretary Lloyd Austin said Tuesday that Washington is sure that an Iran-backed militia is behind an attack on Ain al-Asad air base in western Iraq, where American and coalition forces are stationed.

"Specifically which group, we're still investigating to determine that," Austin told reporters during a joint press conference with US Secretary of State Antony Blinken, Australian Foreign Minister Penny Wong and Australian Deputy Prime Minister and Defense Minister Richard Marles in Annapolis, Maryland.

"The United States will not tolerate attacks on our personnel in the region. We've adjusted our military posture to strengthen our force protection, to reinforce our ironclad commitment to the defense of Israel, and to remain prepared to respond to any contingency," he said.

Austin said he ordered the USS Abraham Lincoln Carrier Strike Group to replace the USS Theodore Roosevelt Carrier Strike Group currently deployed in the Central Command area of responsibility.

Several US personnel were reportedly injured Monday in the attack on the air base.

The US on Friday announced that it would deploy additional military assets to the Middle East amid rising tensions.

"These posture adjustments add to our already broad range of capabilities in the region, and we remain ready to deploy on short notice to meet evolving threats to our security, our partners, or our interests," Austin said.

He added that the US also remains "intensely" focused on de-escalating tensions in the region as well as securing a Gaza cease-fire and hostage-prisoner swap deal.