The United States has called on China to act against Chinese companies which it said were bypassing United Nations sanctions to help Iran with its nuclear programme and missile technology. When the sanctions were passed at the UN earlier this year, Western companies expressed concern that companies pulling out of Iran could leave a vacuum which Chinese firms might try to exploit. A senior US official has confirmed that Washington provided Beijing with a list of Chinese companies it believes are breaching UN sanctions against Iran. The US official said China had pledged it was committed to implementing UN resolutions against Iran. The official also said Washington expected Beijing to take appropriate steps to stop the Chinese companies from helping Iran to improve its missile technology and its nuclear programme.