Two U.S. Navy Seals were missing Sunday after they fell into the water during a nighttime boarding mission off the coast of Somalia on Thursday, officials said.

The incident came as the U.S. has been cracking down on Iranian-backed Houthi rebels in Yemen, who have been attacking commercial vessels in the Red Sea. The Houthis, who control part of Yemen, have hit shipping lanes in the Red Sea and Gulf of Aden 28 times since late November. The Houthis say the attacks are a response to Israel’s invasion of Gaza.

A U.S. official, who spoke on the condition of anonymity to discuss details that have not yet been made public, told the Associated Press the missing SEALs were on a mission not related to Operation Prosperity Guardian, the U.S. and international mission to provide protection to vessels in the Red Sea.

The SEALs were on an interdiction mission, the official said, when one of them fell off a ship after high waves hit the vessel, prompting another SEAL to go after him to attempt a rescue.

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U.S. Central Command said search and rescue operations were ongoing. The command told USA TODAY it won't release more information on the incident until the personnel recovery mission is complete.

The SEALS had been dispatched to approach a suspicious vessel off the Somali coast when the incident occurred, the New York Times reported.

The SEALS' mission was also unrelated to the seizure of a Marshall Islands-flagged tanker by Iran, the Washington Post reported.

Contributing: The Associated Press