North Korea has said it will weaponise its plutonium stocks amid threats to take military action over United Nations sanctions, state media said.

Pyongyang would view any US-led attempts to "blockade" it as an "act of war". The warning from North Korea's foreign ministry was carried by Pyongyang's official Korean Central News Agency (KCNA) on Saturday.

The North Korean foreign ministry statement said: "Firstly, all plutonium to be extracted will be weaponised. One third of used fuel rods have so far been reprocessed.

"Secondly, we will start uranium enrichment," the statement added, cited by the BBC.

On Friday, the United Nations Security Council voted unanimously to impose tougher sanctions on North Korea, after its nuclear test on 25 May.

The North also tested a rocket thought to be capable of carrying a warhead, though Pyongyang said it was designed to carry a satellite.

The UN sanctions include the inspection of North Korean ships, a wider ban on arms sales and other financial measures.

North Korea is thought to possess enough reprocessed plutonium for between six and eight nuclear weapons.

Pyongyang has stated its nuclear weapons programme is purely a defensive measure to protect it against a US attack.