DOHA, Qatar (CNN) -- Six British crewmembers and one American were killed Saturday when two British Navy Sea King search and rescue helicopters collided in mid-air over the Persian Gulf, UK Central Command in Qatar said.

The accident occurred at 4:30 a.m. (8:30 p.m. ET Friday), Pentagon officials said. Three British crew members were aboard each helicopter, the officials said. The identity of the American was not clear.

According to British military sources, the helicopters were involved in fleet defense and were not carrying troops.

A full search and rescue mission began immediately after the crash, coalition officials said.

The helicopters came down in international waters at about 4:30 a.m. Saturday (0130 GMT), shortly after taking off from a British naval ship. Officials said the accident occurred within sight of the ship.

The accident is the second involving coalition forces in two days. On Friday a U.S. Marine CH-46 helicopter crashed in Kuwait, killing all 12 people aboard.

The eight British and four American dead were the first coalition casualties of the war against Iraq.