WASHINGTON, Dec 6 - One US Marine was killed and rescue teams were searching for five others missing after two Marine Corps aircraft collided in mid-air and crashed into the sea off the coast of Japan during a refueling exercise, officials said on Thursday.

Japanese and American officials said they had so far found two of the seven Marines who had been aboard the aircraft, an F/A-18 Hornet fighter jet and a KC-130 Hercules.

"One of the recovered Marines is in fair condition and the other has been declared deceased by competent medical personnel," a US Marine Corps statement said.

The deadly crash is the latest in a string of US military aviation accidents around the world in recent years, which have prompted hearings and criticism in Congress over aircraft safety.

"The aircraft were conducting routine training and aerial refueling was a part of the training," the Marine Corps said, without giving any information on the possible cause of the crash.

The incident occurred around 2 a.m. local time in Japan (1700 GMT Wednesday) about 320 km (200 miles) off the Japanese coast.

"The incident is regrettable, but our focus at the moment is on search and rescue," Japanese Defense Minister Takeshi Iwaya told a news conference. "Japan will respond appropriately once the details of the incident are uncovered."

A US Navy P-8A patrol and surveillance aircraft was helping in search and rescue efforts along with Japanese authorities, the Marine Corps said, adding that the incident was under investigation.

Reuters