North Korea on Saturday threatened it would weaponise all of its plutonium and start enriching uranium in response to UN Security Council sanctions slapped on it for missile firings and a nuclear test.

"Firstly, all plutonium to be extracted will be weaponised. One third of used fuel rods have so far been reprocessed," its foreign ministry said in a statement.

"Secondly, we will start uranium enrichment," it said, adding the North has successfully developed technology needed to enrich uranium after it decided to build its own light water reactors.

It also said it would consider any blockade as an act of war and said it would retaliate militarily.

Earlier, the UN Security Council unanimously adopted a resolution imposing tougher sanctions on a defiant North Korea and targeting its atomic and missile programmes in response to its second nuclear test.

The 15-member body, endorsing a resolution sponsored by Britian, France, Japan, South Korea and the US, condemned the May 25 nuclear test conducted in "violation and flagrant" disregard of earlier Council resolutions.