South Korean Foreign Minister Ban Ki-moon was traveling Monday evening to Beijing on a two-day visit to seek China's cooperation in halting any North Korean launch.

China is the North's key ally and is believed able to exert the most influence on Pyongyang. Beijing has also hosted international talks on the North's nuclear program, which haven't convened since November amid a North Korean boycott in anger over U.S. financial restrictions.

The concerns over a possible North Korean launch have prompted the U.S. to move up its planned test of a missile-detecting radar system in northern Japan, Kyodo News agency reported, citing an unidentified U.S. official in Washington.

A test run of the high-resolution radar, capable of detecting incoming missiles, was initially scheduled to begin weeks later. However, Kyodo said testing could start as early as Monday.

Japanese Defense Facilities Administration Agency, in charge of U.S. military bases in Japan, said the report could not be immediately confirmed.

The so-called X-Band radar had been transferred from a U.S. base in Japan to the Japanese Air Self-Defense Force's Shariki base at Tsugaru, in the country's north. Tsugaru is 360 miles northeast of Tokyo.

The radar deployment is part of the joint missile defense project, which began after North Korea fired a missile, part of which flew over Japan, in 1998.

Tokyo and Washington on Friday also signed an agreement to expand their cooperation on a joint ballistic missile defense shield, committing themselves to joint production of interceptor missiles.

The agreement had been previously negotiated and did not result from emerging fears of a possible North Korean missile test, officials said.

There has been speculation that the U.S. could try to intercept the missile if it is fired.