SEOUL, South Korea – South Korea's chief nuclear negotiator urged North Korea on Wednesday to stick to its pledge to give up its atomic ambitions, as Pyongyang resumed a stalled disarmament process following a breakthrough deal with the United States.

The appeal came as Pyongyang ended a two-month boycott of the disarmament deal after the United States removed the communist regime from a terrorism blacklist as a reward.

“North Korea, which has been accused of repeatedly backing out of promises or demanding more than what it should get, can prove its denuclearization commitment only with actions, not with words,” envoy Kim Sook said in an article in the mass-circulation Chosun Ilbo newspaper.

Later Wednesday, Kim told opposition lawmakers that North Korea has “commenced the disablement work,” but he did not elaborate, according to the main opposition Democratic Party.

On Tuesday, the North allowed U.N. monitors back onto the nuclear site. A diplomat in Vienna familiar with the International Atomic Energy Agency's work there said the agency's three-member team had resumed monitoring Tuesday. He demanded anonymity because he was not authorized to discuss the issue publicly.

State Department spokesman Sean McCormack said the North had begun taking steps to finish disabling the Yongbyon complex. Japan's Kyodo News agency quoted chief U.S. nuclear envoy Christopher Hill as saying, “There has been a resumption of the disabling activity.”

Two months ago, North Korea stopped disabling the Yongbyon nuclear facility in anger over U.S. demands that Pyongyang accept a plan to verify its accounting of nuclear programs as a condition for removal from the terrorism list.

Until late last week, the North had threatened to reactivate the plutonium reprocessing plant at Yongbyon.

Kim told ruling Grand National Party lawmakers that it would be difficult to complete the disabling of the North's nuclear facilities by year's end because the process has been delayed, according to GNP spokesman Cha Myeong-jin.

Kim said he expects the six-nation nuclear talks will resume, but host China has not proposed specific dates yet. The negotiations involve China, Japan, the two Koreas, Russia and the United States.

North Korea alarmed the world in 2006 by setting off a test nuclear blast. It then agreed to dismantle its nuclear program in exchange for energy aid and other concessions.

Associated Press Writer George Jahn in Vienna, Austria, and Desmond Butler in Washington contributed to this report.