ROH

SEOUL, South Korea (AP):

South Korean President Roh Moo-hyun reportedly ordered his government yesterday to send a "grave warning" to North Korea about a threatened nuclear weapons test, a day after China issued its strongest rebuke yet on the matter.

Russian Foreign Minister Sergei Lavrov said that Moscow was working with North Korea to try to dissuade it from a test.

Amid the rising tensions, a United States military plane capable of detecting radiation took off from southern Japan, believed to be part of U.S. efforts to monitor for signs of a possible nuclear test by North Korea, Japan's Kyodo News agency said.

Contingency plan

"We must do everything so that that doesn't happen," Lavrov said at a news conference on a visit to Warsaw. "We are working with the leadership of North Korea to stop steps that could negatively impact the situation."

Roh also ordered the government to draw up a "contingency plan" if the nuclear standoff with North Korea worsens, South Korea's Yonhap news agency said, citing unidentified presidential staff.

At the same time, Roh instructed the South Korean government to step up diplomatic efforts to forestall a North Korean test, the report said.

Top meeting

Roh's orders came after a meeting with his top security adviser, according to Yonhap. Calls to the presidential office went unanswered on the first day of a three-day holiday.

Later in the evening, South Korean Foreign Minister Ban Ki-moon and his Japanese counterpart Taro Aso held a 20-minute telephone call, agreeing that a nuclear test by North Korea is unacceptable and pledging to step up diplomatic efforts to defuse the crisis.

North Korea threatened Tuesday to conduct a nuclear test to prove the country is a nuclear power.

Pyongyang claims it has nuclear weapons and needs them to deter a U.S. attack, but hasn't performed any known test to verify that.

The North's announcement prompted outcry from a host of nations including China, the North's main ally. Beijing's ambassador to the United Nations urged Pyongyang Wednesday not to go ahead with a test, warning of "serious consequences."