Seoul warned Monday that it might shoot down a North Korean rocket if it passes over South Korean territory, as worries about what Washington calls a long-range missile test overshadowed an international nuclear security summit.

Nearly 60 world leaders gathered Monday in Seoul to talk about ways to keep nuclear material out of the hands of terrorists. But North Korea has dominated attention in Northeast Asia since announcing earlier this month that it would send a satellite into space aboard a long-range rocket Associated Press reported.

North Korea calls the launch part of its peaceful space program and says a new southerly flight path is meant to avoid other countries; previous rockets have been fired over Japan. Washington and Seoul, however, say the multistage rocket is meant to test delivery systems for long-range missiles that could be mounted with nuclear weapons.

"We are studying measures such as tracking and shooting down (parts) of a North Korean missile in case they stray out of their normal trajectory" and violate South Korean territory, said Yoon Won-shik, a vice spokesman at the Defense Ministry.

"We cannot help viewing (the launch) as a very reckless, provocative act" that undermines peace on the Korean peninsula, he said.

The South Korean and U.S. militaries know that North Korea has moved the main body of the rocket into a building at a site near the village of Tongchang-ri in North Phyongan province and that it is making preparations for a launch, Yoon said. He said the two allies' militaries are closely monitoring the situation, but he didn't elaborate on the North's preparations.

The Tongchang-ri launch site is about 35 miles (50 kilometers) from the Chinese border city of Dandong. Analysts describe it as a new, more sophisticated site that would allow the North to fire the rocket from the west coast to avoid sending it over other countries.

President Barack Obama and South Korean President Lee Myung-bak urged North Korea in a joint news conference Sunday to immediately stop its launch plans, warning they would deal sternly with any provocation. Obama said the move would jeopardize a deal settled last month in which the U.S. would ship food aid to the North in exchange for a nuclear freeze.

The launch preparations come as North Koreans and new leader Kim Jong Un mark 100 days since the death of Kim's father, Kim Jong Il.

North Korea says its launch is set for sometime around celebrations marking the 100th anniversary of the April 15 birth of late President Kim Il Sung, who was Kim Jong Il's father and the current leader's grandfather.

Obama is also pressuring China to use its influence to press North Korea to put off the launch.

A Chinese government-backed disarmament expert said Monday that the launch shouldn't be allowed to dominate discussions at the summit, in an apparent bid to divert pressure on Beijing to convince Pyongyang to abandon its plans.

"I think North Korea did this to overshadow our talks about nuclear security. We shouldn't fall for their trick," said China Arms Control and Disarmament Association head Li Hong.

China is North Korea's biggest source of diplomatic support and economic assistance, although China says its leverage over Pyongyang is limited by the government's unpredictable nature and Beijing's overriding concern for stability along its northeastern border.

However, in a show of Beijing's worry, China summoned North Korea's ambassador earlier this month to warn of threats to peace in Asia and called on all sides to exercise "cool and restraint."

Chinese President Hu Jintao met with his South Korean counterpart on Monday and "shared concerns" about the rocket announcement, Lee's office said in a statement. South Korea "asked China to actively make efforts for the cancellation of North Korea's rocket launch plans, and the two sides agreed to continue to closely cooperate," it said.

Obama was to meet with Hu later in the day.

The U.N. Security Council condemned North Korea's last long-range rocket launch in 2009. Pyongyang responded by abandoning six-nation nuclear disarmament talks and, weeks later, carrying out a nuclear test, its second.