Beijing on Tuesday downplayed a United Nations report indicating that prohibited missile technology was shared by North Korea and Iran through a third country that diplomats have said was China.

"This so-called 'internal UN document' is a UN expert group report. It does not represent the Security Council's position or the position of the Security Council sanctions committee," the foreign ministry said in a statement.

According to UN diplomats, a Chinese representative on a UN panel of seven experts on North Korean nuclear sanctions refused to sign the report, which said prohibited material was moved through a "neighbouring third country".

The country is not named in the report, excerpts of which were provided to AFP, but diplomats said it was China, isolated North Korea's closest ally.

The ministry declined to address the allegations when asked about them earlier Tuesday during a regular press briefing, insisting only that China was "earnest and responsible in implementing Security Council resolutions".

The UN Security Council imposed sanctions against North Korea after it carried out two nuclear tests in 2006 and 2009. It is banned from dealing in nuclear and ballistic material.

"Prohibited ballistic missile-related items are suspected to have been transferred between the Democratic People's Republic of Korea and the Islamic Republic of Iran on regular scheduled flights of Air Koryo and Iran Air," the report said.

Air Koryo and Iran Air are the national airlines of North Korea and Iran. Iran also faces UN sanctions over its nuclear programme.

Six-nation talks on ending Pyongyang's nuclear weapons drive have been stalled since December 2008, and proliferation fears were heightened last November when the North said it had a uranium enrichment plant.

China has sought to bring North Korea back into the negotiations, which also include South Korea, Japan, Russia and the United States.

The US special envoy on North Korea, Stephen Bosworth, held talks with officials in Seoul on Tuesday.