Q&A: Will Iran nuclear sanctions work?

As top officials at a G8 meeting in Quebec today called for the international community to stop the spread of nuclear weapons, the drumbeat for Iran nuclear sanctions is nearing a crescendo.

"We urge a heightened focus and stronger coordinated action, including sanctions if necessary, on the Iranian regime," said Canadian Prime Minister Stephen Harper today. "Tehran must halt its nuclear activities and engage in peaceful dialogue. There is much at stake."

While Iran remains defiant, the United States and its allies are pushing forward – albeit cautiously, in an effort to balance the desire to punish the Tehran government against concerns that sanctions could undermine the country's opposition Green Movement. The US is now calling for the United Nations Security Council to impose targeted sanctions, and is working to wear down the resistance of other Security Council members, especially Russia and China.

The US accuses Iran of attempting to develop nuclear weapons. Iran insists its program is for peaceful purposes.

What sanctions have already been imposed on Iran?

US economic measures against Iran date to the Islamic Revolution in 1979. The sanctions were increased after Iran was implicated in the bombing of the US Marine Corps barracks in Beirut in 1983 and the US added Tehran to the list of state sponsors of terrorism.

US sanctions included freezing Iranian assets, bans on investment in Iran, and prohibiting the export to Iran of certain products. International suspicion about Iran's nuclear program was piqued in 2002 when uranium enrichment and heavy-water production plants were revealed.

Iran's incomplete cooperation with the International Atomic Energy Agency (IAEA) and failure to comply with a Security Council order to stop uranium enrichment led to three rounds of multilateral sanctions from the Council, beginning in 2006. Those resolutions froze assets of individuals and companies associated with Iran's nuclear program, limited travel by certain individuals, and prohibited the export of nuclear- and missile-related technology to Iran.

What effect did those sanctions have on Iran's nuclear program?

Very little. Analysts agree that the Security Council's previous sanctions have not prevented Iran from making progress in its nuclear program.

The IAEA said in 2009 that Iran had accumulated enough low-enriched uranium to make one nuclear bomb if it was much more highly enriched. In September, Iran said it had constructed a second uranium-enrichment plant unknown to international inspectors. President Mahmoud Ahmadinejad announced in February that Iran had completed its first batch of 20 percent enriched uranium, and had the capability to produce weapons-grade uranium, although he said Iran had not done so.

Iran insists the highly enriched uranium is for use in a medical reactor, but experts say that enriching uranium to such a level is an important step on the way to producing weapons-grade uranium, which must be enriched to 90 percent. A February IAEA report confirmed that Iran had enriched uranium to 20 percent and that the IAEA could not rule out "current" work on weaponization.

What new sanctions are being considered?

Before the Iranian elections last year, Washington had made several diplomatic overtures to Iran. But now the equation has changed.

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