Beijing: A top US envoy said on Wednesday he did not succeed in persuading North Korea to turn over a long-delayed declaration of all its nuclear programs for eventual dismantlement.

"Things are moving ahead, but I'm not in a position to talk about a timetable," US Assistant Secretary of State Christopher Hill said after two days of meetings with North
Korean nuclear envoy Kim Kye Gwan.

Hill was pessimistic when asked whether the disarmament of the North's nuclear facilities was progressing as scheduled.

"Completing everything by the end of the year will be a challenge," he said.

Hill also met with Chinese and Japanese envoys and will head to Moscow on Thursday to meet Russian officials and the South Korean nuclear envoy. All are involved in six-nation talks on North Korea's nuclear programs.

North Korea promised to complete its declaration by the end of last year in exchange for its removal from US terrorism and economic sanctions blacklists, but disagreements over what the declaration would contain delayed the document.

The US had previously insisted that it also include North Korea's alleged uranium enrichment program and nuclear cooperation with Syria.

Washington later backed down from those demands, drawing strong conservative criticism at home.

North Korea has already halted production of plutonium for bombs at its main nuclear facility and begun disabling it under the watch of US officials so that it cannot be easily restarted.

North Korea also gave US thousands of documents from its Yongbyon reactor, which were being reviewed to determine how much plutonium was produced there.