Washington demanded China block shipments of missile parts from North Korea to Iran, according to US documents leaked by WikiLeaks and cited by the Guardian on Sunday.

The British newspaper, citing a diplomatic cable from 2007, said the United States gave China specific details about a shipment that was expected to transit Beijing.

"We... insist on a substantive response from China to this information," said the document published on the Guardian website, marked "secret" and sent by the State Department.

According to the cable, diplomats were instructed to make the request "at the most effective level possible", and express wider 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, saying: "It appears that these shipments did occur and are continuing to transit via Beijing."

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

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

The disclosure comes at a time of high tension on the Korean peninsula following North Korea's artillery strike on the South last week.

China is Pyongyang's sole major ally and has come under increasing international pressure to act in response to the shelling, which killed four people, but has refrained from condemning the North.