Powell met President Roh Moo-Hyun and other top officials on the last leg of a three-nation Asian tour aimed at forging a joint strategy with Tokyo, Beijing and Seoul to get Pyongyang to return to the table unconditionally.

Despite success on his first two stops, North Korea shows no sign of dropping its boycott of the talks and is threatening to bolster its military deterrent to counter "hostile" US acts.

And, just hours after Powell arrived here, South Korean military units were put on their highest state of alert to search for possible North Korean infiltrators after a hole was found in a fence that separates the border.

In both Japan and China, Powell rejected Pyongyang's claims of Washington's aggressive attitude and also dismissed its demands for up-front rewards for returning to the six-party talks.

After being offered a US aid-for-disarmament package at the last round of the Beijing-hosted talks in June, North Korea refused to attend a fourth meeting in September -- citing belligerence by the United States.

Shortly before Powell arrived in South Korea late Monday, a senior State Department official said China had signalled to Powell that it would intensify its efforts to persuade North Korea to rejoin the talks.

"It is my opinion that the Chinese will use their combination of influence and try to get the dialogue to resume as soon as possible and certainly within the next couple of months," the official said on condition of anonymity.

After meeting Chinese President Hu Jintao, Premier Wen Jiabao and Foreign Minister Li Zhaoxing, Powell himself said he was hopeful China would use its influence with North Korea.

"I hope as a result of conversations today, both of us will energize the other members of the six-party framework to resolve the outstanding issues that keep us from setting a date for a meeting," he told reporters in Beijing.

Li said after the meeting that China would talk to North Korea on the matter but stressed that Beijing wanted Washington to show more flexibility, according to China's Xinhua news agency.

"We wish the US side would go further to adopt a flexible and practical attitude on the issue," he said. "China will ... push for a new round of six-party talks at the earliest date"

After Powell's meetings in Japan on Sunday, Tokyo agreed to press Pyongyang to return to the talks during working-level meetings next month with North Korean officials to discuss the Cold War-era abduction of Japanese citizens.

The same day, though, North Korea accused the United States of paying only "lip service" to a peaceful settlement of the nuclear deadlock. It blasted a US-led joint naval exercise off the Japanese coast as a sign of US antagonism.

Pyongyang criticised the exercise again when it began on Monday, denouncing it as an attempt at a maritime blockade and a "serious infringement" of its sovereignty that would dim prospects for a negotiated settlement to the nuclear impasse.

"These moves only make the prospect of the negotiations ... dimmer as the days go by," the official Korean Central News Agency said. "Dialogue can never go together with war exercises."

The drill, which is being held under the auspices of President George W. Bush's Proliferation Security Initiative (PSI), is designed to practice techniques for seizing illicit weapons cargos on the high seas.

Although one stated goals of PSI is to prevent the spread of weapons of mass destruction by and to North Korea, Powell denied the maneuvers were aimed at Pyongyang and said it need only worry if it is involved in illicit shipments.

He also rejected Pyongyang's complaints about a new US human rights law aimed at North Korea, saying the matter was a valid concern and desperate North Koreans were "speaking out" about abuses by fleeing the country.

As Powell began his meetings in China, a group of North Korean refugees proved his point by attempting to enter a South Korean consulate building in Beijing.

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