WASHINGTON (Reuters) - US Defence Secretary James Mattis said on Monday (Aug 21) there would be a wider investigation into US naval operations after American warship USS John S. McCain collided with an oil tanker east of Singapore, leaving 10 sailors missing in the second accident involving a US warship in two months.

"The chief of naval operations' broader inquiry will look at all related accidents at sea, that sort of thing. He is going to look at all factors, not just the immediate ones," Mattis told reporters in Amman, Jordan.

The accident early Monday followed one in June, when the USS Fitzgerald guided missile destroyer collided with a freighter in Japanese waters, killing seven sailors.

The chief of US Navy, Richard Spencer, said the Navy will "fully investigate" the cause of the incident.

"As details continue to emerge, we can be proud of the heroic effort by the crew to tend to the needs of those injured and save the ship from further damage while returning safely to port," he said in a statement.

He also thanked Singapore for its help. "I also want to express my appreciation to the government of Singapore for their swift support and assistance during this time of need," said Spencer.