At the highest levels of the South Korean government, officials were questoning whether North Korea was bluffing when it said Thursday it had made nuclear bombs.

"It was in line with North Korea's previous contention that it has extracted plutonium to produce nuclear weapons. I don't see anything new," Vice Foreign Minister Lee Tae-Sik said.

He described North Korea's claims as part of its tested tactics of brinkmanship to seek more concessions from the United States.

"It appears to be part of (North Korea's) negotiating strategy," he said.

The United States believes North Korea has built nuclear bombs, although no conclusive proof has been produced to corroborate North Korea's claims.

Pyongyang has made similar assertions publicly and privately in the past, and analysts say Pyongyang's latest boast conforms with Washington's assessment that North Korea has developed one or two crude bombs.

"It is very difficult for outsiders to verify their claims. Even in the early 1990s, North Korea was known to have made one or two crude bombs," said Kim Sung-Han at the state-run Institute of Foreign Affairs and National Trade.

The nuclear standoff erupted in October 2002 when the United States accused North Korea of operating a program based on highly enriched uranium.

According to the US side, North Korea privately admitted running the program, only to issue public denials later.

At the opening round of six-party talks in August 2003, the US said North Korea threatened to test nuclear weapons and formally declare itself a nuclear power.

But North Korea was still in public denial. That lasted for two more months, Then in October 2003, the North's foreign ministry said Pyongyang was building up its nuclear deterrent and had completed the reprocessing of 8,000 spent fuel rods, enough plutonium for around six nuclear weapons.

"As the United States has no intention to drop its hostile policy, (North Korea) will consistently maintain and increase its nuclear deterrent force as a just self-defensive means" to repel a US attack, it said at the time.

A similar statement was released just over a year ago in which the Stalinist state once again boasted of its nuclear arsenal.

However, since North Korea expelled international monitors from the International Atomic Energy Agency from its nuclear complex at Yongbyon two years ago, there has been no way to verify such claims.

Though Washington has expressed its view that North Korea has nuclear weapons, South Korean officials have been less certain.

They have said they intend to carry out a detailed analysis of North Korea's intentions before drawing conclusions about the statement.

"After that, we'll exchange views with other countries on the current situation and how to persuade North Korea to come back to six-party talks," foreign ministry spokesman Lee Kyu-Hyung told reporters.

North Korea has attended three rounds of inclonclusive six-nation talks, which also group China, South Korea, the United States, Japan and Russia.

Officials from the ruling Uri Party loyal to President Roh Moo-Hyun voiced doubt about North Korea's nuclear capability saying in a statement Pyongyang was using the nuclear card to seek more concessions from the United States ahead of a new round of talks.

But the conservative Grand National Party, the main opposition group, said North Korea had hoodwinked the South Korean government by building atomic bombs while pretending to engage in reconciliation.

"The North Korean announcement showed how absurd and loose our government's intelligence and measures on North Korea are," the GNP said in a statement.

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