High-ranking senators from both major U.S. political parties are urging prompt action to stem Iran's development of nuclear capabilities. The statements come as Iran continues to defend its right to have a nuclear program and to call for continued diplomatic efforts to resolve the matter.

Arizona Senator John McCain says Iran's nuclear ambitions constitute the gravest situation facing the United States since the end of the Cold War, aside from the September 11, 2001 terrorist attacks. Speaking on CBS's Face the Nation program, the Republican member of the Senate Armed Services Committee said it is time to bring the matter before the U.N. Security Council.

"We must go to the U.N. now for sanctions. If the Russians and the Chinese, for reasons that would be abominable, do not join us, then we would have to go with the willing," said McCain. "There is only one thing worse than the United States exercising a military option, that is a nuclear-armed Iran."

Senator McCain acknowledged that the U.S. military is stretched thin in Iraq and elsewhere, but said the United States must keep a military option on the table when it comes to dealing with Iran.

"Let us be honest," he said. "We are tied up to a great degree [militarily in Iraq]. But that does not mean that we do not have military options. We do. To say that under no circumstances would we exercise military options would be crazy."

Iran recently announced it was restarting nuclear research and development. It has long maintained that it only aims to provide for the country's growing energy needs. Iran's leaders have questioned the right of major nuclear powers to dictate what other nations may do in pursuing peaceful nuclear technology.

In a rare news conference Saturday, Iranian President Mahmoud Ahmadinejad said Iran would not abandon its nuclear program, even if the matter is referred to the U.N. Security Council.

A Democrat on the Senate Armed Services Committee, Indiana's Evan Bayh, says that Iran cannot be trusted. Speaking on CNN's Late Edition program, the senator pointed to recent statements by Iranian President Ahmadinejad calling for the eradication of Israel and calling the Holocaust a "myth" as evidence of extremism and irrationality on the part of Iran's leadership.

"Iran is the foremost sponsor of terrorism in the world. Iran is a menace. They have to be dealt with. Appeasement will not work. Nice words will not work," said Senator Bayh. "We need to use diplomacy, economic sanctions, other means so that we will not have to resort to military action. But the time to act is now. We [the United States] have been in denial for four long years."

Senator Bayh accused the Bush administration of having largely ignored the threat posed by Iran until now. Last week, President Bush described anti-Israeli statements from Tehran as "unacceptable" and said that Iran's development of nuclear weapons would give them the capability to go from words to actions against the Jewish state. He said Iran must not be allowed to possess a nuclear weapon.