The Pentagon is investigating the cause of a crash of an American military surveillance drone off the coast of Yemen on Monday morning, two U.S. officials said.

The officials, speaking on the condition of anonymity to discuss operational matters, confirmed that the drone, an MQ-9 Reaper, fell out of the sky. Iranian-backed Houthi militants said on Monday that they had downed the drone near the port city of Al Hudaydah, in western Yemen.

“Yemeni air defenses were able to shoot down an American plane (MQ-9) with a suitable missile while it was carrying out hostile missions against our country on behalf of the Zionist entity,” a Houthi military spokesman, Yahya Sarea, said in a statement.

“Yemeni armed forces will not hesitate to take more military measures and carry out more qualitative operations against all hostile targets in defense of beloved Yemen,” the statement said.

If the Houthis’ claims are confirmed, this will have been the second time the group has shot down an American drone since the Oct. 7 Hamas attack on Israel, and Israel’s response, plunged the region into crisis.

The downing of a Reaper drone, the mainstay of the American military’s aerial surveillance fleet, is another escalation of violence between the United States and Iran-backed groups in Yemen, Iraq and Syria. The episodes have intensified over the past two months, underscoring the risk that the conflict between Israel and Hamas could spiral into a wider war.

The United States struck five Houthi military targets, including an undersea drone, in Houthi-controlled areas of Yemen on Saturday, according to a statement from the military’s Central Command.

The use of the underwater drone is believed to have been the first time that the Houthis have employed such a weapon since they began their campaign against ships in the Red Sea and the Gulf of Aden on Oct. 23, the statement said.

The Houthis say the attacks are in solidarity with Palestinians who have been living under Israel’s retaliatory attacks in Gaza.