U.S. Navy helicopters returned fire and and sank three small boats carrying Houthi militants in the Red Sea on Sunday, after U.S. warships responded to a distress call from a merchant vessel, military officials said.

A Maersk container ship, the Singapore-flagged Hangzhou, issued a distress call at about 6:30 a.m. local time, U.S. Central Command said in a statement on Sunday. The merchant vessel said four small boats were attacking it.

“The small boats, originating from Houthi-controlled areas in Yemen, fired crew-served and small-arms weapons at the Maersk Hangzhou, getting to within 20 meters of the vessel, and attempted to board the vessel,” Central Command said.

Helicopters from two U.S. ships — the USS Eisenhower and the USS Gravely — responded and issued verbal calls to the small boats, U.S. officials said.

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