US and South Korean troops on Thursday completed computerised joint war games denounced by North Korea, but field training involving a US aircraft carrier will continue through next month.

The allies launched their annual Key Resolve/Foal Eagle drills on February 28, some three months after the North's deadly shelling of a South Korean border island.

They completed the 11-day Key Resolve drill, which focused on computer-based simulations, without incident despite North Korean threats to turn Seoul into a "sea of flames" in the event of any military provocation.

The Foal Eagle exercise involves field training that will continue until April 30, military officials said. The two exercises involve a total of 12,300 US troops and some 200,000 South Korean service members including reservists.

US officials said the nuclear-powered USS Ronald Reagan and its strike group would arrive in South Korea this month.

South Korean officials said there would be a major sea drill involving the group but did not say whether it would enter the Yellow Sea, which China considers "sensitive waters".

The US and South Korea say the exercises are defensive in nature while training their forces to respond to any provocation. North Korea habitually denounces them as a rehearsal for invasion.

Tensions are high after the island attack, which killed two marines and two civilians.

The South also accuses its neighbour of torpedoing a warship near the disputed Yellow Sea border in March 2010 with the loss of 46 lives, a charge Pyongyang denies.