US President Barack Obama demanded yesterday that North Korea halt a "provocative" missile launch, as tensions 'flared bri'the possible eve of a test sure to spark a dangerous new foreign policy crisis.

Obama spoke sharply and directly to the Stalinist state during a joint press conference with French President Nicolas Sarkozy, after South Korea predicted the aggressive North Korean move could come within hours.

"We have made very clear to the North Koreans that their missile launch is provocative," Obama said, ahead of the 60th anniversary Nato summit here.

"It puts enormous strains on the six-party talks ... they should stop the launch," he said, referring to the negotiations aimed at dismantling Pyongyang's nuclear programme.

"The response so far from the North Koreans has been not just unhelpful, but has resorted to the sort of language that has led to North Korea's isolation in the international community for a very long time.

"Should North Korea decide to take this action, we will work with all interested parties indie international community to take appro--'1 priate steps to let North Korea know that it can't threaten the safety and security of other countries with impunity."

Earlier, South Korean President Lee Myung-Bak said in London that the North was on the verge of firing the rocket, which it says is carrying a satellite, but which its foes see as a test of the long-rangeTaepodong-2 missile.

Lee told reporters that Seoul would be ready to send an envoy to its northern neighbour if the reclusive state's leaders were willing to accept one.

Asked when South Korea expected the rocket to be fired, Lee said it depended on weather conditions.

"If tomorrow's weather is suitable for them, if they think it's suitable for them to test fire this missile then it's going to be tomorrow," he said.