The United States and South Korea began annual military exercises on Monday as reunions of families separated by the Korean War continued in North Korea, a media report said.
The exercises Key Resolve and Foal Eagle went ahead despite demands from Pyongyang that they be stopped, the Yonhap News Agency reported.
North Korea earlier threatened to scrap the reunions running between February 20 and 25 if the manoeuvres were not called off, but later agreed to let the meetings go ahead.
The reunions are the first since 2010.
Key Resolve was due to last two weeks and involve 10,000 South Korean personnel and 5,200 members of US forces.
Foal Eagle involves 7,500 US troops and is due to continue until mid-April.
Around 200,000 South Korean troops took part in Foal Eagle last year but fewer are involved this year due to their deployments tackling bird flu and snow removal.
Pyongyang regularly accuses the US and South Korea of planning an attack with their manoeuvres, an accusation both countries deny.
The manoeuvres were to be “low key” because of the continuing reunions, Yonhap quoted a South Korean military official as saying.
The US has about 28,500 troops stationed in South Korea.