He said South Korea's National Intelligence Service also suspected that the Stalinist state reprocessed part of its stockpile of spent nuclear fuel rods that will yield plutonium for nuclear bombs, reported Agence France-Presse (AFP).

Ko told the National Assembly's intelligence committee there had been some 70 high-explosive tests at Yongdok, 40 kilometers (25 miles) northwest of Yongbyon, North Korea's nuclear complex north of the capital city Pyongyang.

Experts said conventional high-explosives are used to trigger atomic blasts by compressing the plutonium core.

"We have also noticed high-explosive tests being conducted in Yongdok district in Gusong City in (the northwestern province of) North Pyongan and we have been keeping track of the movement," Ko was quoted as saying by a senior parliamentary aide.

The new development came as a North Korean delegation arrived in Seoul Wednesday for high-level talks but the agenda covering cooperation and exchanges was immediately overshadowed by the crisis over Pyongyang's nuclear weapons program.

No sooner had the delegation set foot on South Korean soil than Seoul's spy chief made his shocking revelations.

The North Korean delegation, in an arrival statement, stressed the danger of nuclear war.

"These high-level talks are taking place at a time when tensions on the Korean peninsula are higher than ever before," the statement said.

"The dark clouds of a nuclear war are coming toward the Korean peninsula moment after moment."

The statement urged the South Koreans to live up to the spirit of an inter-Korean joint declaration for peace signed in 2000 and to cooperate with North Korea to head off the danger of war.

"I expect good results," said Kim Ryong-Song, a senior North Korean minister who is leading the five-member delegation to the ministerial talks which will open in earnest Thurday and last until Saturday.

In a separate related development, South Korean President Roh Moo-Hyun sought to reassure North Korea Wednesday that it would get the support it needs to haul itself into the modern age provided it abandoned a quest for nuclear arms.

Roh warned the Stalinist regime that pursuing its nuclear ambitions jeopardized the future of Northeast Asia.

"No country should be alienated in Northeast Asia but in the same context, no nation has a right to threaten the security of neighboring states and the stability of the region," he said in a speech at Beijing's prestigious Tsinghua University.

"It (North Korea) has to choose the path of peace and coexistence with others. No nation in the international community believes that the nuclear project will assure its future. "North Korea must dismantle its nuclear project."

South Korea and China said in a joint statement issued late Tuesday that a nuclear free and stable Korean peninsula was paramount to its future development.

"The two sides are also convinced that the nuclear issue in the Democratic People's Republic of Korea (North Korea) could be settled through talks," the statement said, without specifying whether they should be in a bilateral or multilateral context.

Roh said Wednesday that he sincerely hoped that Pyongyang would choose to "join the ranks in the march toward peace and prosperity".

"When North Korea discards its nuclear program and comes forward onto the path of dialogue and openness, the rest of the world will not spare the support and cooperation it needs," he said.

Continuing a thread he has been weaving since his arrival in China Monday, Roh stressed the need for Northeast Asia to move forward to keep pace with a rapidly changing, globalized world.

While he acknowledged that past conflicts in the region had created suspicions that still exist "as an open sore", Roh urged people to push on and consider the future.

"Now, the course of Northeast Asian history should be changed," he said.

"We should not repeat the past history of invasion and forced control. The scars of confrontation and conflict should be healed and a new order of cooperation and unity put in place."

Nine months ago, North Korea sparked a security crisis when it said it was running a clandestine nuclear weapons program, according to Washington. Efforts to resolve the crisis have so far failed.

Tension has mounted since North Korea kicked out international nuclear inspectors and withdrew from the Non-Proliferation Treaty.

Pyongyang has also claimed reprocessing of spent fuel rods was under way but U.S. and South Korean officials have said until now they were unable to confirm the claim.

"We suspect that North Korea has recently reprocessed a small portion of the 8,000-odd fuel rods at the Yongbyon nuclear facility," Ko was quoted as saying by an aide to opposition party lawmaker Chung Hyung-keun.

U.S. and South Korean officials say North Korea may have one or two nuclear bombs and believe reprocessing of spent fuel rods at its Yongbyon plant would yield enough plutonium for around six more.

North Korea has never tested a nuclear device, but indicated last month that it possessed atomic weapons when it said in a foreign ministry statement that it intended to "build up its nuclear deterrent."