North Koreans are known as tough, intimidating negotiators who use threats and bluster to get what they want.

North korean negotiators blurted out a threat to turn Seoul into a "sea of fire" in 1994 and 10 years later told US negotiators they would test or even sell nuclear bombs unless they got their way.

The outside world has been negotiating on-and-off with the isolated Stalinist regime for five decades since the end of the 1950-53 Korean war.

According to its harshest critics, North Korea has never signed an agreement it didn't intend to break and never accepted an international obligation it hasn't violated.

So there were few gasps of surprise when Pyongyang looked ready to jettison a statement it had signed only hours earlier at the end of the fourth round of six-party talks in Beijing.

In Monday's statement it said it would scrap its nuclear weapons and programes, return to the nuclear Non-Proliferation Treaty and accept international inspectors in return for concessions from the Unite States.

Then on Tuesday it added a deal-breaker -- it must have light-water reactors first.

North Korea's move recalled the famous U-turn in 2003 at the end of the first round of six-party talks in Beijing when it said the talks were useful -- then abruptly pronounced them dead and not worth resurrecting.

In September last year North Korea failed to show up for an entire round of talks it had pledged to attend, citing US "hostility."

Top US and South Korean officials shrugged off the North's remark this time as typical bluster designed to maximize its demands before the parties meet again in November for serious talks to flesh out the statement of principles.

"This is simply the North Koreans starting the negotiations early," said a State Department official in Washington.

North Korean-watchers have cautioned all along that Pyongyang should not be taken at its word.

"It goes without saying that we should never trust North Korea to keep its side of the bargain," the Nautilus Institute, a US think tank on global issues, said in a 2003 report.

Other North Korean-watchers discount the value of negotiations.

Nicholas Eberstadt of Washington's American Enterprise Institute views North Korea as a kleptocracy supporting leader Kim Jong-Il and his henchmen.

They "make a deal, break the deal, then demand a new deal for more, issuing threats until you get what you want," he said in a commentary.

Scott Snyder, senior associate of the Asia Foundation and author of a book on North Korean negotiating tactics, said US counterparts had found that North Koreans "will keep agreements."

But they tend to do so on their own terms and "obligations are interpreted by the North Korean side as narrowly as possible ..., adhering to the letter of the law and otherwise challenging both the spirit and terms of implementation of specific agreements."

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