The United States has asked Beijing to do more to stop Chinese companies from providing assistance and expertise to Iran's efforts to develop nuclear weapons and more powerful missiles, The Washington Post reported late Sunday.

According to the newspaper, the Obama administration believes several Chinese companies are violating United Nations sanctions against Iran. An anonymous U.S. official told the paper that Robert Einhorn, the State Department official who oversees the enforcement of sanctions against Iran, gave a "significant list" of such companies and banks to Chinese officials last month.

The U.S. official did not name any of the Chinese companies or say how many were on the list. But he told the Post that U.S. intelligence believes several Chinese companies and banks were involved in providing restricted technology to Iran, mostly for its missile program.

A second official, also speaking anonymously, told the Post that Chinese companies had been discovered selling Iran material that could be used to make better centrifuges. Those are used to enrich uranium that could be used in a nuclear device.