US President Barack Obama demanded on Friday that North Korea halt a "provocative" missile launch, as tensions flared on 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 in Strasbourg.
"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 in the international community to take appropriate 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-range Taepodong-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.
"If the weather does not permit it, then I suspect it's going to be some other day."
He criticised North Korea's plan to fire a costly rocket at a time when it was suffering chronic food shortages which had left the country in a "dismal situation".
"I think it is important for the North Koreans to realise and fully understand that it is not in their benefit for them to test fire this missile," Lee said.
"Perhaps in the short-term it might give them an upper hand in the negotiations but in the long-term, their trust given to them by the international community will only lessen."
Lee and Obama, who met on Thursday on the sidelines of the G20 economic summit in London, have both warned they will seek swift United Nations action if the Stalinist state goes ahead with the launch, as has Japan.
"The presidents said the international community needs to take stern, unified action against North Korea if the North fires a long-range rocket," a South Korean official told AFP on condition of anonymity on Thursday.
An Obama administration official said any launch would see the United States respond firmly at the UN, adding that "there is no daylight" between Seoul and Washington on the issue.
Another official said "considerable" efforts had been made by other members of the six-party talks process to convince North Korea to step back from the brink of launching the rocket.
The six-party forum involves, China, Japan, South Korea, Russia, the United States and North Korea itself.