Fearing that some Chinese firms may be helping Iran to improve it's missile technology and develop nuclear weapons, US has asked Beijing to stop such companies from helping Tehran. A State Department official, who overseas the enforcement of sanctions against Iran, gave a significant list of such companies and banks to Chinese officials last month. The Washington Post reported that the Obama administration believes that several Chinese companies are violating United Nations sanctions against Iran. The Post said, a Chinese Embassy spokesman said his country would investigate the US charges.