SEOUL (Reuters) - South Korea told its communist neighbor on Wednesday to stop a barrage of insults and threats which it said were adding to tension across one of the world’s most heavily militarized borders.

South Korean President Lee Myung-bak talks to government officials at the Presidential Blue House in Seoul April 1, 2008. REUTERS/Park Chang-ki/Yonhap

Hermit North Korea, unsettled by the new South Korean president’s demands it show more respect for human rights and uphold its part of an international denuclearization deal, has shown its outrage through furious rhetoric and, last week, a missile test.

“Your random slander and tension-raising moves are not benefiting peace and stability on the Korean peninsula and we strongly ask you to immediately halt such acts,” the Defence Ministry said in letter to its North Korean counterpart.

Since the two governments are technically at war and have no direct contact, the letter had to be sent by fax from the United Nations Command on the so-called Demilitarised Zone (DMZ) which divides the Korean peninsula.

The increasingly frosty exchanges have cast a shadow over the “sunshine policy” of previous Seoul governments of the past decade, which ensured massive aid flows to the impoverished North for little in return apart from the hope of stability.

They also come as North Korea has been dragging its heels over a promise to make a full disclosure to the international community of everything it has been doing to develop a nuclear arsenal in return for aid and an end to its isolation.

“We are really running out of time,” chief U.S. envoy to the North Korea nuclear talks, Christopher Hill, told reporters after talks with South Korean foreign ministry officials in Seoul.

NUCLEAR DEAL DELAY

North Korea has threatened to cut off dialogue with Seoul and demanded an apology after the head of its Joint Chiefs of Staff last week said it would hit the North’s nuclear weapons base if it attacked but had no plan for a pre-emptive strike.

Some analysts say Pyongyang may be using the attacks to try to deflect blame for its delay in implementing the nuclear deal -- which major powers hope will eventually lead to its complete atomic weapons disarmament.

But they say it is likely to be restrained from taking the fiery rhetoric into something more dangerous by China, its only significant ally and which has no interest is North Korea adding to its problems ahead of the Beijing Olympic Games, its launching party as a world power.

North Korea has also blamed the nuclear agreement delay on the United States and some analysts have said Pyongyang, with its long record of brinksmanship over the nuclear issue, may be hoping to squeeze a last concession out of President George W. Bush before his term ends.

On Tuesday, the North’s official media in its first public acknowledgement that Lee Myung-bak was South Korea’s new leader, described him by name with a string of insults.

And it derided new President Lee’s offer of substantial investment in the North, which has come with the condition that Pyongyang’s government mend its ways.

But the latest war of words has had little impact in the South. Its financial markets, long used to angry rhetoric across the border, have largely ignored the latest expressions of hostility.

It also appears to have barely touched the campaigning for next week’s election for the National Assembly when Lee’s party is expected to win a majority.