SEOUL, June 13 (AFP): A defiant North Korea vowed Saturday to build more nuclear bombs and to start enriching uranium for a new weapons programme after the UN Security Council imposed sanctions over last month's nuclear test.

The North, describing Friday's sanctions resolution as a "vile product" of a US-inspired campaign, said it would never abandon nuclear weapons and would treat any attempt to blockade it as an act of war.

The 15-member Council voted unanimously Friday to slap tougher sanctions on the North to cripple its nuclear and ballistic missile programmes.

Washington hailed the measure but warned that Pyongyang might respond with "further provocation."

The hardline communist state, in a foreign ministry statement reported by its official news agency, said all new plutonium it extracts would be weaponised.

One third of used fuel rods from the Yongbyon reactor have so far been reprocessed into weapons-grade plutonium, it said.

"Secondly, we will start uranium enrichment," it said, adding the North had successfully developed the necessary technology.

In 2002, the North denied US claims that it was operating a secret uranium enrichment programme in addition to its admitted plutonium-based operation.

The plutonium-producing plants were shut down under a six-nation disarmament deal in 2007. But the North vowed to restart them after the Security Council in April condemned its long-range rocket launch.

"It has become an absolutely impossible option for the DPRK (North Korea) to even think about giving up its nuclear weapons," the statement said, adding it would consider any blockade as an act of war and would retaliate militarily.

The North said it never wanted nuclear weapons "but it was an inevitable course of action forced upon us by the US hostile policy and nuclear threats."

"No matter how hard the US-led hostile forces may try all sorts of isolation and blockade, the DPRK, a proud nuclear power, will not flinch from them."

Resolution 1874 passed Friday, which does not authorise the use of force, calls on UN member states to expand sanctions imposed after the North's initial nuclear test in October 2006.