North Korea must respect all its relevant international obligations Russian Foreign Ministry Igor Ivanov

Pyongyang's ally said the Stalinist state should stick to its international agreements, but also warned the US against inflaming tensions.

Later the US said it was up to North Korea to change its course or "pay a serious price".

Moscow's comments followed North Korea's hint that it could also pull out of the nuclear Non-Proliferation Treaty if the confrontation over its alleged nuclear programme continues.

The North has already expelled inspectors from its nuclear power plant at Yongbyon and is threatening to restart the facilities.

"Pyongyang's decision [to reactivate the reactor]... cannot help but provoke regret," said Russian Foreign Minister Igor Ivanov in a statement.

CRISIS CHRONOLOGY

16 Oct: N Korea acknowledges secret nuclear programme, US announces 14 Nov: Fuel shipments to N Korea halted 12 Dec: N Korea threatens to reactivate Yongbyon plant 22 Dec: N Korea removes monitoring devices at Yongbyon reactor 26 Dec: UN says 1,000 fuel rods have been moved to the plant 27 Dec: N Korea says it will expel UN nuclear inspectors

Timeline of tensions

Mr Ivanov said Moscow wanted to help salvage a agreement signed in 1994 between North Korea and the US, under which Pyongyang agreed to freeze its nuclear programme.

But he warned: "This can only be achieved through constructive dialogue. Aggressive rhetoric and threats, and attempts to isolate North Korea can only escalate tensions, which will not help regional and international stability."

The US says it is not planning to attack North Korea, but does favour a "tailored containment" strategy which could include economic sanctions on Pyongyang.

On Monday, President Bush's spokesman said Pyongyang was isolating itself by its actions which threatened food and other forms of aid needed by North Korea.

"The entire world stands ready to help North Korea, but North Korea will not realise any of the benefits and the help that they need until they reverse [their] current course," Scott McClellan said.

"The international community has made clear that North Korea's relations with the outside world hinge on its termination of its nuclear programme."

Isolation v engagement

The US has urged the United Nations to consider imposing sanctions on North Korea.

But South Korea's President Kim Dae-jung said on Monday that isolating Communist states did not work, and he would continue his policy of engagement with Pyongyang.

"The more stalled relations are, the more effective this sunshine policy is. We cannot go to war with North Korea and we can't go back to the Cold War system and extreme confrontation," he said.

North Korea's latest move is an apparent threat to withdraw from the Non-Proliferation Treaty.

Last time it pulled out of the treaty, nine years ago, there was a dangerous confrontation with Washington, before the deal known as the Agreed Framework was signed.

A statement from the North Korean foreign ministry, carried by the North's KCNA news agency on Sunday, said that the US had begun "ditching" the 1994 pact, "thus putting this special status of ours in peril".

Under the Agreed Framework, North Korea agreed to freeze its nuclear programme in exchange for fuel and aid.

But in November, Washington halted the fuel shipments because, it said, Pyongyang had admitted it was resuming its nuclear programme.

In December, North Korea unsealed the Yongbyon plant and began moving nuclear fuel rods there.

North Korea continues to demand direct talks with the US. Its stated aim is to sign a non-aggression pact with a country it sees as a direct military threat.

But the BBC's Charles Scanlon in Seoul says the US is concerned that formal negotiations would be seen as rewarding bad behaviour.

NORTH KOREA NUCLEAR PROGRAMME

Yongbyon: Five-megawatt experimental nuclear power reactor and partially completed plutonium extraction facility. Activities at site frozen under 1994 Agreed Framework Taechon: 200-MWt nuclear power reactor - construction halted under Agreed Framework Pyongyang: Laboratory-scale "hot cells" that may have been used to extract small quantities of plutonium Kumho: Two 1,000-MWt light water reactors being built under Agreed Framework

Analysis: North Korea's nuclear progress