US freezes N Korea firms' assets

N Korea's known nuclear programme is based around its Yongbyon plant

The US has moved to freeze the assets of two North Korean companies in an effort to enforce sanctions against Pyongyang over its nuclear development.

The General Bureau of Atomic Energy and the Korea Tangun Trading Corp were both deemed to be supporting North Korea's nuclear and missile programmes.

North Korea says it is in the final stages of uranium enrichment, bringing it closer to making a nuclear weapon.

The UN passed tougher sanctions after a nuclear test by Pyongyang in May.

That move prompted North Korea to withdraw from six-party talks about its nuclear programme.

The US said the sanctions against GBAE and Tangun would come into effect immediately, with assets under US jurisdiction frozen and US persons prohibited from doing business with them.

Both firms had been blacklisted by the UN in July.

A US official told Reuters news agency the sanctions were a clear signal the US was seeking to increase pressure on North Korea to return to the six-party talks.

The unnamed official said Pyongyang had been "making nice noises" but that there were "concerns that they may be moving forward on their nuclear activities".

Ample reserves

Last week, North Korean state media reported that the country had entered the final stage of uranium enrichment, which would give it a second way to produce a nuclear weapon.

The nuclear test conducted in May this year and an earlier test in 2006 were both believed to have used plutonium.

The worry is that uranium enrichment is a process that can be easily hidden. In addition, North Korea has ample natural reserves of the raw material, says the BBC's John Sudworth in South Korea.

North Korea's plutonium programme is based at the Yongbyon reactor, which is under US satellite observation.

Observers say the US has long suspected the existence of a secret uranium enrichment programme in the North, though experts say it remains little-developed.