North Korea, under international pressure to return to nuclear disarmament talks, vowed Friday never to give up its atomic arsenal in return for economic aid.

The communist state's official news agency instead demanded an end to what it called US hostility -- apparently restating a call for a formal peace treaty on the Korean peninsula.

Seoul's military said separately the North had declared live-fire zones near its disputed sea border with South Korea, raising the prospect of a further display of firepower after shelling in late January heightened tensions.

The North has also moved some multiple rocket launchers to bases along its west coast, a spokesman for the Joint Chiefs of Staff (JCS) told AFP. It was unclear whether this was part of a military drill or a permanent move.

Chinese and North Korean negotiators held talks in Beijing last week about restarting the six-party nuclear forum, which the North quit last April.

The two sides also discussed possible economic assistance, South Korea's Yonhap news agency has reported. Some analysts believe the North will eventually have to return to dialogue given its worsening economy and acute food shortages.

The North has developed atomic bombs for its own defence, "not to threaten anybody or receive economic favours or rewards", the Korean Central News Agency said in a commentary.

It is a "misjudgement" if the outside world thinks it will dump nuclear bombs in return for economic benefits, the agency said.

"Unless (the US) terminates its hostile policy and nuclear threats towards our republic, our abandonment of nuclear weapons will not happen even if the earth breaks."

Pyongyang, which tested atomic weapons in October 2006 and May 2009, has set two conditions for resuming the nuclear dialogue: the lifting of UN sanctions and a US commitment to discuss a formal peace treaty.

The 1950-53 war ended only in an armistice.

The North says it developed nuclear weapons to defend itself against a potential US attack, and it must have a peace treaty with Washington before it considers handing them over.

Pyongyang has previously spurned Seoul's offer of massive economic aid in return for denuclearisation.

In late January, after declaring two "no sail" zones, the North fired 370 artillery shells into the Yellow Sea near the contested border over three days.

It said it was staging a routine exercise but South Korea and the United States described the firing as provocative.

The North has now declared four exclusion zones in the Yellow Sea -- including two near the border -- and two in the Sea of Japan (East Sea) off its northeast coast, South Korea's military said.

They will be effective for three days from Saturday. "Currently, there is no unusual military activity detected in the North," a JCS spokesman said.

The Yellow Sea border was the scene of deadly naval battles in 1999 and 2002 and of a firefight last November that left a North Korean patrol boat in flames.

Since that clash the North has positioned dozens of the rocket launchers, with a range of 60 kilometres (37 miles), at its coastal bases near the maritime frontier, Yonhap news agency said.

The JCS spokesman gave no figure for the number of rocket launchers deployed.