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Andrei Lankov, an expert on the region at Kookmin University in Seoul, believed the six-party talks would resume "sooner or later" but suggested they were largely irrelevant to the current crisis, because the real question was whether and when South Korea and the US would provide more aid to the North. "This is a protection racket – you pay the local toughs, and if you don't your windows are going to be broken," he said.

Relations on the peninsula deteriorated sharply when Lee took office in 2008 and cut off free-flowing aid to the North. But Tuesday's attack marked a new level of hostility. The North said that civilian deaths "if true … [are] very regrettable", but blamed the South for using its citizens as human shields. It also accused the US of setting up Tuesday's incident to justify today's drills.

The drills are the largest of their kind yet, according to the South's Yonhap news agency, involving an aircraft carrier carrying 75 planes and at least four other warships. But US military officials said the training was routine and no live-fire exercises were planned. According to South Korean media they are taking place far south of the disputed maritime border.

Pyongyang's National Peace Committee said in a statement that the manoeuvres were creating "a state of ultra-emergency". It also renewed its threat of "merciless counter-military strikes", although it often makes similar warnings ahead of such exercises.

Yonhap said North Korea had moved surface-to-surface missiles to frontline areas, but military and government officials said they could not comment.

"It is impossible to confirm the report as it is classified as a military secret," one told Reuters.

An unidentified government source also told Yonhap that the North had deployed surface-to-air missiles along its western coastline, apparently targeting fighting jets near the disputed Yellow Sea border.

Yesterday, South Korea's marine commander vowed "thousand-fold" revenge if the North attacked again.

Earlier today the South Korean government ordered journalists to leave Yeonpyeong for safety reasons, but bad weather forced it to abort an attempted evacuation, leaving about 400 people there.