Seoul - The United States' top negotiator with North Korea was cautious Tuesday over any predictions ahead of his trip to Pyongyang to break an impasse in implementing a nuclear disarmament agreement.

"We will see what happens when we go up to DPRK (North Korea) tomorrow," Hill told reporters upon arriving in South Korea before driving over the inter-Korean border to Pyongyang.

Hill is seeking to persuade North Korea to reverse moves earlier this month to revive work at its main nuclear site Yongbyon in steps that have threatened to derail a 2007 pledge to abandon nuclear weapons.

"We need to make sure that we are going to be able to verify their declaration," he said.

North Korea started work at Yongbyon and has informed UN inspectors from the International Atomic Energy Agency (IAEA) that it intends to begin processing plutonium.

Pyongyang said the move was taken because the US did not meet its end of the deal by removing the Stalinist state from a terrorism blacklist, which Hill said the US is ready to consider.

"And what we also want to do is to move on and complete our obligations in the phase two which includes, of course, taking them off the terrorism list," said Hill in Seoul.

Washington insists that a deal must first be reached on a process to verify North Korea has fully revealed all aspects of its nuclear programme and a process for implementing the 2007 agreement. (dpa)