A senior U.S. official says Washington believes that Chinese companies are helping Iran to improve its missile technology and develop nuclear weapons without Beijing’s approval.The Washington Post reports that the anonymous official said the Obama administration has asked China to put a stop to such activity.The newspaper said the request was conveyed during a visit to Beijing last month by a U.S. delegation led by Robert Einhorn, the State Department’s special adviser for nonproliferation and arms control.The official told the Post that China is the only country with a major oil and gas industry that is prepared to deal with Iran. He said everyone else has pulled out to abide by U.N. sanctions – Voanews