Washington  - The United States is sending its top negotiator with North Korea to Pyongyang this week to break an impasse in implementing the nuclear disarmament agreement, the State Department said Monday.

US Assistant Secretary of State Christopher Hill is due to arrive in Seoul on Tuesday and later in Beijing for discussions with his South Korea and Chinese counterparts before heading to North Korea.

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.

"The effort is to find out why North Korea has taken the steps that it's taken. And we want to see those steps reversed," State Department deputy spokesman Robert Wood 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.

North Korea took the steps after complaining the United States has not met its end of the deal by removing the Stalinist state from a terrorism blacklist.

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)