President Barack Obama called Thursday's historic meeting between Iran and the U.S. over the Islamic Republic's nuclear program a "constructive beginning," but suggested real progress would begin when Iran's words matched its deeds.
Earlier Thursday, a top U.S. official met with Iran's top atomic negotiator on the sidelines of high stakes, six-nation talks on Tehran's nuclear program.
Obama gave Iran two weeks to grant international inspectors "unfettered access" to its secret nuclear facility.
"Talk is no substitute for action," Obama said from the White House after talks ended earlier in the day in Switzerland. "Our patience is not unlimited."
The meeting comes after years of attempts by the U.S. to persuade the Islamic Republic to halt its nuclear development program.
The U.S. along with five other world powers are also considering new and tighter sanctions against Tehran -- just in case the negotiations fail.
''We'll see if the Iranians are prepared to start a process that could lead to them being re-integrated into the international community of nations, or if whether they choose a path of isolation," said U.S. National Security Council spokesman Mike Hammer. "They have a choice to make here."
However, British intelligence officials say they have evidence that Iran is in the final steps of acquiring a nuclear weapons capability.
According to Britain's Financial Times newspaper, Iran resumed its nuclear arms program four years ago.
Meanwhile, dozens of Christian leaders, including Christian Broadcasting Network chairman Pat Robertson, Rev. John Hagee, and the current and past presidents of the Southern Baptist Convention are urging tough economic sanctions on the Islamic Republic.
In a letter to Congress, they warn that a nuclear Iran could pose a significant threat to an already volatile Middle East. And that neighboring nations "have reason to fear the religious, political and military ambitions of Iran's extremist leaders."