The United States and South Korea on Tuesday wrapped up military drills at the centre of soaring tensions with North Korea, as Pyongyang ignored a new overture over a flagship joint industrial zone.

The two-month-long "Foal Eagle" air, ground and naval field training exercise -- which involved more than 10,000 US troops along with a far higher number of South Korean personnel -- had infuriated Pyongyang.

"The drill is over but the South Korean and US militaries will continue to watch out for potential provocations by the North, including a missile launch," Seoul's defence ministry spokesman Kim Min-Seok told reporters.

The North is still maintaining a number of missiles and missile launchers that were recently moved to its east coast in apparent preparation for a launch, Kim added.

The Korean peninsula has been in a state of heightened military tension since the North carried out its third nuclear test in February.

Relations between the two Koreas have been further soured by a row over the Kaesong factory park inside the North that was once a rare symbol of inter-Korea cooperation.

Most remaining South Korean workers quit the complex early on Tuesday, but seven supervisors stayed to resolve administrative issues. It was unclear when they would return.

The North did not respond to a plea by South Korean businessmen to visit Kaesong Tuesday for talks aimed at averting its permanent closure, according to Seoul, despite hopes of an easing of tensions after the end of the drills.

Pyongyang regularly denounces joint US-South Korean exercises as a rehearsal for invasion, but Seoul and Washington have insisted the recent manoeuvres were defensive in nature.

"With the military drills over, at least we can worry less about any accidental clash developing into a full-scale war," said Paik Hak-Soon, a North Korea expert at the Sejong Institute, a think-tank in Seoul.

He said a planned summit in Washington on May 7 between the US President Barack Obama and South Korean leader Park Geun-Hye -- who took office in February -- could be more significant in setting the tone for inter-Korean relations.

"If the North finds the outcome of the summit unsatisfying or unacceptable, that means we would have to live in constant fear of another military provocation near the border," Paik said.

Incensed by fresh UN sanctions and the joint South Korea-US military exercises, the North has spent weeks issuing blistering threats of missile strikes and war.

The Foal Eagle exercises "are the main factor of pushing the situation on the Korean Peninsula to the brink of a nuclear war", the newspaper of the North's communist party, the Rodong Sinmun, said on Monday.

"The US and South Korean warmongers should bear in mind that they will not be able to escape a miserable doom if they ignite a nuclear war against the DPRK in the end," it added.

But after weeks of apocalyptic threats, the North's state media has in recent days also reported on North Korean leader Kim Jong-Un's visits to a football match and a health complex with his wife, in what was seen as a sign of easing tensions.

Pyongyang has regularly accused the United States of preparing to launch a nuclear strike on its territory, and reacted furiously to the use of nuclear-capable B-52s and B-2 stealth bombers in the joint South-US drills.

"This year's exercise was far more aggressive and public in nature than previous drills," Lee Jae-Joung, who served as the South's unification minister from 2006 to 2008, said in a radio interview.

"That prompted the North to take a more aggressive stance in turn, sparking the whole cycle of escalating tensions," Lee added.

South Korea's Yonhap news agency reported on Sunday that North Korea appeared to be preparing for a major live-fire military exercise of its own involving artillery units and air force jets.

A North Korean artillery attack on a South Korean island in November 2010 killed four people. Seoul also holds Pyongyang responsible for the sinking of one of its naval vessels with the loss of 46 sailors the same year.