China has warned its partners on the UN Security Council that it intends to block publication of a report on the status of North Korea's nuclear program, a diplomat at the United Nations said Friday.

"A Chinese expert has signed this report, but China does not want it published," said the diplomat, who spoke on condition of anonymity.

The UN report outlines North Korea's progress on the isolated regime's controversial uranium enrichment program, and calls for tougher implementation of sanctions, according to the diplomat.

"Many countries want this report to be released, but China does not want it," the official said.

The report, the broad outlines of which are already known, will be discussed next Tuesday at an expert-level meeting of the Security Council, according to the diplomat.

The report says North Korea has at least one secret nuclear military site, and the subterfuge work was probably started in the 1990s without raising suspicions, according to diplomats who have seen the document.

It is based on evidence from US scientist Siegfried Hecker, who was taken to a secret site by the North Korean authorities last November.

Hecker has told of seeing hundreds of centrifuges when he went to the Yongbyon complex -- considered the backbone of North Korea's military nuclear program. The report quoted him as saying North Korea must have had foreign help to build the facility, one diplomat told AFP on condition of anonymity.

The United States and other Western nations among the Security Council's 15 members have called for tougher sanctions on Pyongyang.

North Korea claims to possess an atomic bomb and has conducted two nuclear tests, in 2006 and 2009.