The United State alone cannot force Iran to give up its nuclear ambitions, Defense Secretary Robert Gates said Monday.

Gates called Iran as "an ambitious and fanatical theocracy," and said he has yet to find "the elusive Iranian moderate," according to remarks prepared for delivery at the Jewish Institute for National Security Affairs.

"With a government of that nature, only a united front of nations will be able to exert enough pressure to make Iran abandon its nuclear aspirations — a source of great anxiety and instability in the region," Gates said.

Iran denies it is pursuing nuclear weapons. It says its nuclear program is strictly for civilian energy development.

"Our allies must work together on robust, far-reaching and strongly enforced economic sanctions," Gates said. "We must exert pressure in the diplomatic and political arenas as well. And, as President Bush has said, with this regime we must also keep all options on the table." The term "all options" is a veiled reference to possible military action.

Gates said Iran seems increasingly willing to act contrary to its own interests.

"We should have no illusions about the nature of this regime or its leaders — about their designs for their nuclear program, their willingness to live up to their rhetoric, their intentions for Iraq, or their ambitions in the Gulf region," he said in his prepared remarks, copies of which were made available before he spoke.