Seoul, Jan. 19: The military establishment in North Korea has admitted over the weekend that it had "weaponised" enough plutonium for roughly four to six nuclear bombs.

The New York Times quoted scholar Selig Harrison as saying that North Korean officials had revealed this fact to him, certifying what US intelligence officials have already said that North Korea had harvested enough fuel for six or more bombs.

Harrison, however, said the officials had not defined what "weaponised" meant, but the implication was that they had built nuclear arms.

In the wake of this announcement, the paper says that South Korea has ordered its military to heighten vigilance along its heavily fortified border with North Korea.

This was confirmed by a spokesman attached to the South Korean military joint chiefs of staff.

South Korea has also told its fishermen to refrain from sailing near North Korean waters, a day after the North Korean military declared an "all-out confrontational posture" against the South and threatened it with a naval clash.

On Saturday, North Korea's Foreign Ministry said the country would maintain its "status as a nuclear weapons state" as long as it perceived a nuclear threat from the United States.

The North conducted a test of a nuclear device in 2006, but it appeared to result in a fizzle and experts concluded the explosion was relatively small.

While the country has often claimed to possess a "deterrent," this appears to be the first time it has quantified how much plutonium it says it has turned into weapons.

According to the NYT, North Korea's saber-rattling toward the South has increased in intensity since President Lee Myung-bak took office in Seoul a year ago with a vow to take a tougher stance on North Korea, reversing 10 years of his liberal predecessors' efforts to engage the North with economic aid.

With President-elect Barack Obama about to take office and negotiations over the North's nuclear program expected to resume, it is possible that the North is merely setting up its negotiating position.

But analysts say the North's remarks could also be an indication that it was intending to hold onto its arms despite an agreement it signed with five countries including the United States in 2005, in which it committed to eventually giving up any nuclear weapons. The exact conditions under which it would do so were left vague.

Harrison, the scholar, presented North Korea's claims of weaponization on Saturday in Beijing after returning from North Korea's capital, Pyongyang.

Harrison, a former journalist who is the director of the Asia program at the Center for International Policy, has traveled several times to North Korea to meet with senior officials there. (ANI)