Pyongyang accused Seoul on Monday of plotting to topple its regime as relations again soured, while a top Chinese official met North Korea's leader to bring the country back to nuclear disarmament talks.

In another blow for inter-Korean ties, the two sides failed to agree on restarting a tourism project.

A statement from North Korean security ministries said Seoul's plots against the country had "recently gone beyond the danger line" and Pyongyang had a secret strike force for protection.

The communist North often claims that Seoul's conservative government is plotting against it.

"We have world-level ultra-modern striking force and means for protecting security which have neither yet been mentioned nor opened to the public in total," the ministries said in a statement on official media.

The North criticised efforts by the South's military to defend the disputed Yellow Sea border — where the North fired artillery salvoes late last month — and its "reckless" operations to destabilise the North.

It complained about "the daily escalating" scattering of propaganda leaflets by balloon, which were now penetrating deep into the country from border areas.

Despite the tough talk, the North has been pushing to revive business projects with the South since it was hit by tougher sanctions for its missile launches and nuclear test last year.

The two sides held talks on Monday about a possible resumption of tours which previously earned the cash-strapped state tens of millions of dollars a year.

Seoul suspended the trips after soldiers in July 2008 shot dead a Seoul housewife who strayed into an off-limits military zone at the Mount Kumgang resort in the North.

South Korea's unification ministry demands safety guarantees before it restarts them.

But spokesperson Chun Hae-Sung said Monday's meeting in the North Korean border town of Kaesong ended "without any significant agreement" after Pyongyang rejected Seoul's terms.

Chun said South Korea demanded that its officials conduct an on-site probe into the shooting but "the North Korean side said it has already conducted sufficient investigations into the incident".

The South also demanded the North guarantee the safety of future tourists. The North said such steps were taken when Kim Jong-Il met last August with a South Korean businesswoman whose company runs the tours.

About 1.9 million visitors, mainly South Koreans, have visited the Seoul-funded Kumgang resort since it opened in 1998. Over a decade the tours earned the North a total of $487-million.

The head of the Chinese Communist Party's international department, Wang Jiarui, meanwhile met North Korean leader Kim Jong-Il, Pyongyang's official Korean Central News Agency said.

Wang also met communist party official Choe Thae-Bok to reaffirm the countries' friendship and exchange views "on other issues of common concern," Beijing's Xinhua news agency said.

The meetings came one day before Lynn Pascoe, top political adviser to UN chief Ban Ki-moon, was due in Pyongyang for a four-day visit.

China hosts the six-party nuclear talks which its ally North Korea quit last April, a month before staging a second nuclear test.

As conditions for returning to the nuclear forum, the North wants a US agreement to hold formal peace talks and a lifting of UN sanctions.

In an apparent conciliatory gesture to Washington, Pyongyang on Saturday freed a US missionary who had crossed the border last 25 December on a lone campaign to publicise rights abuses.

AFP

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