South Korea announced Thursday it would ban the entry of people from North Korea who are part of Pyongyang's nuclear weapons program, the first step taken by Seoul to adhere to UN sanctions.

The decision came after North Korea said any action by Seoul under the UN resolution would "drive the inter-Korean relations to a catastrophe" and would be "a grave provocative act" which could lead to war.

US President George W. Bush said Pyongyang's threats were aimed only at dividing the five nations that have been in talks with North Korea on ending its nuclear program.

"What he's doing is just testing the will of the five countries that are working together to convince him there is a better way forward for his people," Bush told a news conference on Wednesday.

He also reiterated that the United States would keep up diplomatic efforts to end the crisis.

But other US officials have not ruled out other options.

Underscoring fears about North Korea, a South Korea lawmaker, quoting from a Defence Ministry report, said North Korea might have extracted enough plutonium for up to seven nuclear weapons.

Pyongyang was also working to miniaturize nuclear devices to fit on ballistic missiles, the report said. North Korea conducted a series of ballistic missile tests in July.

Estimates of the North's nuclear arsenal have ranged from one or two weapons to as many as 10 or more. Its plutonium stockpile is believed to be enough for 13 bombs, according to some estimates.

The South Korea's Unification Minister Lee Jong-seok said Seoul would take action against the North beyond the UN Security Council resolution that mandated trade and financial sanctions.

"The government will ban the passage and stay (in the South) of persons and their family designated by (the UN Security Council) sanctions committee," Lee told a parliamentary committee.

Searching ships

The UN Security Council voted on October 14 to impose financial and arms sanctions on North Korea after its nuclear test earlier this month, but how those measures will be implemented remains a matter of debate.

China, Russia and South Korea urged caution in dealing with the crisis.

The United States, Russia, China, Japan and South Korea are all members of stalled six-party talks with North Korea.

Travel between South Korea and North Korea is already tightly regulated despite a sharp increase in the number of people in South Korea who visit the North on business and on tours.

But the move could have a significant impact on Seoul's future ties with the North because it might affect key North Korea officials who take part in bilateral talks, said Yoo Ho-yeol, an expert on the North at Korea University.

Unification Minister Lee said Seoul would also invoke a maritime agreement with the North to search North Korea ships that make port calls in the South.

Seoul has been cautious about taking steps against the North, out of concern it could escalate tension on the Korean Peninsula and hurt bilateral ties that it had worked hard to build over the past six years.

But Seoul has said it would not be business as usual after the October 9 nuclear test.

Many people in South Korea, however, favor a more conciliatory policy. Former President Kim Dae-jung urged the United States to make "a bold decision" and accept Pyongyang's long-standing demand for direct talks.

"I hope President Bush makes the right decision now," Kim said in a column in the International Herald Tribune Thursday.

But Washington said this was not possible until Pyongyang returned to the stalled Six-Party Talks.

(China Daily October 27, 2006)