South Korea's president sought to galvanize support from world leaders to pursue U.N. Security Council punishment for North Korea if it proceeds with a rocket launch that is suspected to be a cover for a missile test.

President Obama is expected to join the push for a joint response when he meets with South Korea's Lee Myung-bak on Thursday. But it will be harder to convince President Hu Jintao of China, the North's only major ally, on Friday.

Click to view photos | Satellite image of the launch area

In one-on-one meetings Wednesday in London ahead of the G-20 summit, Lee stressed the need for a "united response" among world leaders after Pyongyang carries out what it has said will be a satellite launch some time from Saturday to following Wednesday.

The U.S., South Korea and Japan believe the reclusive country is really testing its long-range missile technology, and they warn Pyongyang would face sanctions under a U.N. Security Council resolution that bans the country from any ballistic activity.

But Beijing and Moscow — veto-wielding permanent members of the Security Council — could object to an attempt to seek sanctions against, citing legal uncertainty over the wording of the resolution because it makes "no mention of launches relating to peaceful outer space activities," the Brussels-based International Crisis Group said in a report.

North Korea has refused to back down and issued warnings of its own, telling the U.S. it will shoot down any spy planes that intrude into its territory and threatening Japan that any effort to intervene in the launch would be considered an act of war.

"If the brigandish U.S. imperialists dare to infiltrate spy planes into our airspace to interfere with our peaceful satellite launch preparations, our revolutionary armed forces will mercilessly shoot them down," South Korea's Unification Ministry quoted North Korean radio as saying.

It is unclear what capability the North Korea has to shoot down high-flying Boeing RC-135s, which can reach altitudes of nearly 10 miles.

U.S. military officials in Seoul declined to comment on the spying allegations or the North's threat.

Lee and Japanese Prime Minister Taro Aso, meanwhile, reaffirmed their intention to take North Korea to the Security Council after the launch.

Lee also assured Aso that South Korea supports Tokyo's right to take action to defend itself, Sakashita said.

Japan has deployed battleships with antimissile systems off its northern coast and stationed Patriot missile interceptors around Tokyo to shoot down any wayward rocket debris that North Korea has said might litter the area.