The United States believes some Chinese firms are helping Iran improve its missile technology and develop nuclear weapons and has asked Beijing to prevent such activity, The Washington Post reported late Sunday.

Citing an unnamed senior US official, the newspaper said the request was conveyed during a visit to Beijing last month by a US delegation led by Robert Einhorn, the State Department's special adviser for nonproliferation and arms control.

Einhorn gave his Chinese counterparts a "significant list" of companies and banks that the United States thinks are violating UN sanctions against Iran without authorization from the Chinese government, the report said.

US intelligence believes that several Chinese companies have been providing restricted technology and materials to Iran's military programs while some Chinese banks were backing these deals, the paper noted.

Most of the deals concerned Iran's missile program, according to The Post.

A senior official from a Western intelligence agency said Chinese firms were also discovered selling high-quality carbon fiber to Iran to help it build better centrifuges, which are used in enriching uranium, the paper noted.

In 2008, for example, Iran obtained 108 pressure gauges, which are critical to the functioning of a centrifuge, from one Chinese company, The Post said.

The report said a year earlier, a small company in the Chinese port city of Dalian provided Iran with a range of sensitive materials, including graphite, tungsten copper, tungsten powder, high-strength aluminum alloys and high-strength steel, again for its nuclear program.

That firm allegedly received payment from Iran via US banks, the paper said.

"My government will investigate the issues raised by the US side," The Post quoted Wang Baodong, a spokesman for the Chinese Embassy in Washington, as saying.