SEOUL, South Korea >> Seoul warned Monday that it might shoot down a North Korean rocket if it strays into 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 for a conference meant 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.

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 it’s 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, across the Yalu River from North Korea. Analysts describe it is 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 in which the U.S. would ship food aid to the North in exchange for a nuclear freeze.

Earlier Sunday, Obama made a symbolic visit to the tense, heavily armed border dividing the Koreas, six decades after the Korean War ended with a cease-fire that leaves the peninsula technically at war.

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.