Will international pressure work on Iran?

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

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 programme was piqued in 2002 when uranium enrichment and heavy-water production plants were revealed.

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

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

The International Atomic Energy Agency (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 per cent enriched uranium, and had the capability to produce weapons-grade uranium, although he said Iran had not done so.

What new sanctions are being considered?

The US has proposed UN sanctions that would target the Revolutionary Guard and concentrate on insurance, shipping, and banking in Iran.

While Russia has shown increasing willingness to support new sanctions, China remains opposed. Both nations hold veto power. Iran is the second-largest supplier of oil to China, which has large investments in Iran's energy sector.