Influential US Senator John McCain told America's allies Saturday that the military option could not be ruled out if diplomatic efforts fail to stop Iran developing a nuclear bomb. "Every option must remain on the table," McCain told an international security conference. "There's only one thing worse than military action, that is a nuclear armed Iran." The Arizona Republican said allies "need to stay united to answer this grave challenge." McCain warned that an attempt by Iran to develop such weapons could spark a nuclear arms race in the Middle East and appealed for Russia and China to back tough action against the Islamic Republic in the UN Security Council. "It is in the interests of Russia and China to support these moves, notwithstanding their business interests," McCain said. "Surely they do not want to see a nuclear armed Middle East."