North Korea has dismissed as "laughable" moves by the United States to impose fresh sanctions following its fifth nuclear test.

Pyongyang said the US must recognise it as a "legitimate nuclear weapons state" and that it would continue to strengthen its nuclear power "in quality and quantity" despite the west's condemnation of the programme.

"The group of Obama's running around and talking about meaningless sanctions until today is highly laughable," North Korea's state-run KCNA news agency cited a foreign ministry as saying in a statement.

"(President Barack) Obama is trying hard to deny the DPRK's (North Korea's) strategic position as a legitimate nuclear weapons state but it is as foolish an act as trying to eclipse the sun with a palm."

The spokesman defended the test as a necessary response to what he described as "augmented threats of nuclear war from the United States".

The robust response comes two days after the secretive communist state - which has been subject to sanctions since 2006 - carried out its fifth and biggest atomic test in defiance of UN sanctions.

It claimed it had detonated a nuclear warhead - ratcheting up a threat its rivals and the United Nations have been powerless to contain.

Pyongyang is facing a further round of international sanctions following the detonation, which triggered an earthquake with a magnitude of 5.

The US, South Korea and Japan are seeking "the strongest possible" measures in response to "the provocative and unacceptable behaviour by the North Koreans".

'Exasperated'

But North Korean leader Kim Jong-Un remains defiant in pursuing a nuclear programme.

The ruling party's newspaper Rodong Sinmun has warned "gone are the days... when the US could make a unilateral nuclear blackmail against the DPRK".

It has also suggested the US is becoming "exasperated by the strong military steps being taken by the DPRK".

In a meeting in Seoul on Saturday, South Korean Foreign Minister Yun Byung-se said Friday's test showed North Korea's nuclear capacity had reached a "considerable level".

After its fourth test in March, sanctions were toughened to include North Korea's mineral trade and stricter banking restrictions.

However, this has not stopped the isolated, impoverished state from conducting a further 21 ballistic missile launches.