Barack Obama warned North Korea yesterday that it would face international action if it went ahead with its launch of a rocket, as Japan made nervous preparations for it to pass over its territory as early as today.

“We have made very clear to the North Koreans that their missile launch is provocative,” President Obama said after a meeting in Strasbourg with President Sarkozy of France.

“Should North Korea decide to take this action, we will work with all interested partners in the international community to take appropriate steps to let North Korea know that they cannot threaten the safety and stability of other countries with impunity.”

He added: “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 international isolation in the international community for a very long time.”

Mr Obama did not specify the kind of action that would be taken and, with the launch predicted in a matter of hours, diplomats were struggling to find ways of responding.

Batteries of Patriot missiles were on standby in northern Japan after reports that the rocket had been fuelled at the Musudanri launch site in the northeast of North Korea. Japanese villages under the flight path set up emergency communication links with the Cabinet office in Tokyo for the unlikely event that the rocket falls short of its intended target and strikes Japanese territory.

North Korea insisted that it is the vehicle for a peaceful communications satellite, not a missile, and has threatened war in response to any attempt to shoot it down. The bulb-shaped tip of the rocket, which was observed on satellite photographs, suggests that it probably is a communications satellite but such technology can also be used for missiles.

Japan, the US and South Korea said that even a satellite launch would breach UN resolutions passed after the last launch in 2006.

“Our top priority is to have the Security Council convened and Japan will aim to reach a consensus that the launch violates the UN Security Council resolution,” Takeo Kawamura, the Japanese Chief Cabinet Secretary, said.

No government is more nervous than Japan, which has taken elaborate precautions against the small chance of an incursion across its borders. According to warnings given by Pyongyang to shipping and aviation, the rocket will be fired across the northern part of the main Japanese island, Honshu.

It is believed to be the latest version of the missile known as the Taepodong 2, a three-stage rocket with a range of 4,200 miles that could potentially reach Alaska or Hawaii. The first stage of the rocket is intended to fall into the Sea of Japan 80 miles from the coast, the second in the Pacific Ocean.

Domestic flights will be diverted and teachers have been ordered to keep radios and televisions on at all times in case of emergency announcements.

“We believe a flying object from North Korea is unlikely to land in our territory,” Sukeshiro Terata, the governor of Akita prefecture, said. “Yet, we must be prepared just in case.”

Times Recommends

• Should Knox’s trial even have reached the courtroom?
• 'Was it real?' The US bailout nightmare
• Iranian opposition plays the long game