Western nations on Tuesday raised concerns about "loopholes" in North Korea nuclear sanctions in the first UN Security Council talks on a report which said the North was sharing missile technology with Iran.

China has objected to the report, which implies that the banned dealings are being carried out through China. But it has asked for more time to decide whether to formally block publication, diplomats said.

Portugal's UN ambassador Jose Filipe Moraes Cabral, who chairs the UN North Korea sanctions committee, said the report's allegations were "serious" but that the Security Council could not agree whether to make it public.

"Shipping and transportation loopholes" need closing, said one British diplomat during the talks. Germany is "concerned" about the nuclear and missile proliferation, added a Germany envoy.

European members of the Security Council have said they would support increasing the number of North Korea individuals and entities subject to sanctions.

The confidential report by a panel of experts, obtained by AFP, accuses North Korea of illegally exporting ballistic missiles, components and technology to countries in the Middle East and South Asia.

"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.

"In an effort to get hard currency and advance its own programs, the country has been actively engaged in the export of complete systems, components and technology to numerous customers in the Middle East and South Asia," it added.

North Korea is also about to complete work on a new launch site for long-range missiles at Donchang-ri on its west coast, the experts said.

The UN Security Council imposed sanctions against North Korea after two nuclear tests in 2006 and 2009. It is banned from dealing in nuclear and ballistic material while a trade embargo includes even sending luxury goods to the North.

But the isolated North has announced a number of breakthroughs in recent months, including the establishment of a uranium enrichment plant. This could give it a new way to make atomic bombs in addition to its plutonium stockpile.

The new report said that the ballistic technology was being shipped through a "neighboring third country". The country is not named but diplomats said it was China.

Diplomats said that Western nations on the 15-member Security Council had pressed for the report to be released as soon as possible. China has previously blocked sanctions reports on North Korea and Sudan.

Beijing on Tuesday downplayed the report. "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," said a Chinese foreign ministry statement.

Iran's foreign ministry rejected the suspicions that it had exchanged ballistic missile expertise with North Korea as "propaganda and fabrications."