By Jacob Gronholt-Pedersen and Ahmed Elimam COPENHAGEN/DUBAI/CAIRO (Reuters) -U.S. helicopters repelled an attack by Iran-backed Houthi militants on a Maersk container vessel in the Red Sea, sinking three ships and killing 10 militants, according to accounts by American, Maersk, and Houthi officials on Sunday. The naval battle occurred around 0330 GMT on Sunday as the attackers sought to board the Singapore-flagged Maersk Hangzhou, Maersk and U.S. Central Command (CENTCOM) said. Helicopters from the USS Eisenhower and USS Gravely joined the ship’s security team in repelling the attackers after…