US intelligence believes Iran has obtained advanced missiles from North Korea that could strike Europe, according to US documents divulged by WikiLeaks and cited by the New York Times Sunday.

The documents also show frustration among US diplomats who have been pressing for China to block shipments of missile parts from North Korea to Iran, Britain's Guardian newspaper reported.

The New York Times, citing a diplomatic cable dated February 24, said "secret American intelligence assessments have concluded that Iran has obtained a cache of advanced missiles, based on a Russian design."

Iran obtained 19 of the North Korean missiles, an improved version of Russia's R-27, from North Korea, the cable said, and was "taking pains to master the technology in an attempt to build a new generation of missiles."

At the request of US President Barack Obama's administration, the New York Times said it had agreed not to publish the text of that cable.

"The North Korean version of the advanced missile, known as the BM-25, could carry a nuclear warhead," said the newspaper, adding it had a range of up to 2,000 miles (more than 3,000 kilometres).

"If fired from Iran, that range, in theory, would let its warheads reach targets as far away as Western Europe, including Berlin. If fired northwestward, the warheads could reach Moscow," it said, referring to other dispatches.

"The cables say that Iran not only obtained the BM-25, but also saw the advanced technology as a way to learn how to design and build a new class of more powerful engines," said the Times.

However, analysts say there is no confirmation of whether North Korea has the technology to miniaturize its nuclear weapons into a missile warhead.

In its report, the Guardian cited a "secret" 2007 diplomatic cable from the State Department giving China specific details about a missile parts shipment that was expected to transit Beijing and demanded a "substantive response."

The document said diplomats were instructed to express US concerns "at the highest level possible".

"The US believes that the proliferation of missile technology between North Korea and Iran will increase and that these two countries will attempt to conduct these transfers through Chinese territory," the document read.

It listed 11 alleged deliveries of missile-related jet vanes from North Korea to Iran that it said were shipped through Beijing's airport on North Korean and Iranian commercial airliners.

The document pointed out that then US president George W. Bush had previously raised the issue directly with Chinese President Hu Jintao.

The cable said the shipments violated UN Security Council resolutions regarding both Iran and North Korea, as well as China's own export-control rules.

It was not known whether the demand led to action by Beijing, said the Guardian, which like the New York Times was given advance access to the WikiLeaks documents.

China's foreign ministry did not immediately respond to an AFP request for comment.

China is an ally of both Iran and North Korea. It is a major importer of Iranian oil, and is the leading backer for the isolated North Korean regime.

The Guardian cable also indicated US testiness over previous requests for Chinese interdiction and said the volume of such missile trade was expected to grow "dramatically."

It said Chinese officials claimed their investigations had found no evidence of such trade. But the cable added "it appears that these shipments did occur and are continuing to transit via Beijing."

US diplomats were instructed to "explain to Chinese officials that the US carefully reviews the intelligence material that we have on shipments before we share it, and we ask that Chinese authorities respect this and act on our information accordingly and appropriately."