Two members of the Navy SEALs remained missing on Saturday after a mishap two days ago while they were attempting to board a ship off the coast of Somalia, two current and two former Pentagon officials said.

The incident comes as the United States is stepping up actions against Iranian-backed Houthi fighters in Yemen, intent on curbing their attacks on commercial vessels in the Red Sea. As part of those missions, the U.S. Navy and allies have been responding to distress calls.

Over the past two days, the U.S. and allies have struck Houthi-linked targets in Yemen, trying to damage the militia’s offensive capabilities.

In the latest incident, the members of the SEAL team were dispatched on Thursday to approach a suspicious vessel off the Somali coast, the officials said. It was unclear on Saturday what prompted the commandos to single out the vessel for a closer investigation.

In recent weeks, the Houthi militia and Somali-based pirates have threatened or seized ships in the Red Sea, the Gulf of Aden and off the Somali coast. The Houthis say they are acting in solidarity with Palestinians in Gaza, who have been under siege by the Israeli military following Hamas’s Oct. 7 attack on Israel. Pentagon officials said on Saturday that the circumstances surrounding this incident were different from those involving the Houthis or pirates. But they declined to disclose further details.

As two members of the SEAL team tried to board the vessel Thursday night in rough seas, one of the commandos apparently slipped off the boarding ladder, according to one current and one former Pentagon official briefed on the incident. Another member of the team then jumped into the water to try to rescue the sailor, the officials said. Both soon disappeared in the swells.

The officials spoke on the condition of anonymity to discuss operational matters.

Navy ships and aircraft were immediately dispatched to the scene, where search and recovery efforts have been underway, the officials said. The military’s Central Command noted the rescue operations in a statement on Friday, but made no mention of the sailors being members of a SEAL team or any details of the incident.

Military officials have started the process of notifying the families of the commandos involved in the episode, a former official said.