He said a peace treaty would only be discussed once North Korea comes back to the six-nation disarmament talks and takes steps on abandoning its nuclear programme.

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However North Korea says the resumption of the nuclear talks depends on building confidence between Pyongyang and Washington, which can be achieved by starting talks on a peace treaty and lifting UN-backed sanctions.

"If confidence is to be built between [North Korea] and the US, it is essential to conclude a peace treaty for terminating the state of war, a root cause of the hostile relations," the country's foreign ministry said in a statement carried by state-run media.

Such a measure is necessary to "bring back the process for the denuclearisation of the Korean Peninsula on track," it said.

North Korea has long demanded a peace treaty, but neighbouring South Korea remains suspicious that it is using the issue as a distraction.

Still at war

The US and North Korea have never had diplomatic relations because the 1950-53 Korean War ended in a truce, not a peace treaty, leaving the peninsula technically still at war over the past five decades.

North Korea, the US-led United Nations Command and China signed a ceasefire, but South Korea never did.

Agreements at the six-nation nuclear talks in 2005 and 2007 envisaged discussion of a peace treaty but only in return for North Korea's full denuclearisation, but the North also said on those occasions that a peace pact should come first.

North Korea has also offered to resume negotiations if the sanctions against it are lifted.

However, speaking at the state department PJ Crowley rejected the idea, saying that the US is "not going to pay North Korea for coming back to the six-party process".