A statement is expected imminently from the US Marines following reports that an American military helicopter crashed near the North Korean border.
French news agency AFP said a CH-53 Sea Stallion helicopter was taking part in a joint drill with South Korean allies when the incident occurred but reported no casualties.
The Yonhap news agency said the helicopter came down in Cheorwon province, which borders North Korea.
More top news
Labour strongholds tended to remain so - apart from a major loss for the party in Dudley.
Labour suffered a "terrible" defeat in Rhondda but has already won 16 Welsh Assembly seats as it looks to record a fifth term in office.
UKIP have made further gains in the local elections in the Anglia region and the Conservatives have won back control in Peterborough.