As the US seeks support at the UN Security Council for new sanctions against Iran, Tehran continues to defy the international community, saying its nuclear program has peaceful not military aims. The controversy has triggered a debate on whether new sanctions will be effective or whether military action is needed.
Despite international pressure, Iran continues to ramp up its nuclear program, enriching uranium at levels that are said to be closer to weapons grade.
And that has Washington experts debating the course that world powers should take.
John Bolton was UN ambassador under President George W. Bush:
"If you consider that the options we have are the use of preemptive force or Iran with nuclear weapons, you can see why military force unfortunately has to be on the table," he said.
Although Bolton says a pre-emptive strike is the only choice, the international community has been focused on maintaining diplomatic pressure on Iran and on winning agreement on new sanctions.
British Foreign Minister David Miliband spoke during a visit to China on Monday
"Britain and China haven't only agreed on the goal that Iran should respect the non-proliferation treaty and not become a nuclear weapon state. We've also agreed on the means to achieve that, which is a combination of engagement and pressure," said Miliband.
New sanctions against Tehran could target Iranian insurance firms and banks and impose travel bans on more individuals, but Russia and China are still reluctant.
Israel is at the opposite end. It feels directly threatened by Iran and has been pushing hard for tough action. Officials there have said all options are on the table, implying that includes a military strike.
But recently, Prime Minister Benjamin Netanyahu also endorsed new sanctions.
"The stronger those sanctions are, the more likely it will be that the Iranian regime will have to choose between advancing its nuclear program and advancing the future of its own permanence," said Netanyahu.
George Perkovitch of the Carnegie Endowment for International Peace says even if sanctions don't work, Iran has to know that it will pay for its behavior.
"It may not change your behavior, but there is a cost for this action," he explained. "And, in part, we want to communicate to other states, other actors who may be looking at what you are doing as a model."
The possibility of regime change in Iran has been raised by some experts. But Perkovitch says that with the Revolutionary Guard more powerful than ever, one question remains.
"....how the Revolutionary Guard actually would get replaced in Iran, put out of business, lose power, so that you have a genuine regime change in Iran," he added.
With the US heavily committed in Iraq and Afghanistan, Washington's ability to exert military pressure on Iran is questionable, says Flynt Leverett at the New America Foundation.
"And even if at this point we want to project large amounts of conventional military power into the Persian Gulf or anywhere else, we are going to have to do it on borrowed money," he said.
The Obama administration is favoring sanctions, experts say, because the other choices are worse.
But they say it's unclear whether Iran's nuclear ambitions - civilian or military - can be contained in the long run.