The United Nations Security Council has imposed sanctions on Iran because of its nuclear activities.
What is Iran doing?
Iran is trying to develop the technology of enriching uranium.
This is done by converting uranium ore into a gas which is then spun through centrifuges to separate the richer parts that can be used as fuel in a nuclear power station.
Why are there objections to this?
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Because this technology can also be used to spin the uranium gas for longer in order to get an even higher level of enrichment and this highly enriched uranium can be used as the basis of a nuclear bomb.
What sanctions has the Security Council imposed?
It has told all member states not to supply Iran with any equipment or technology that could help its uranium enrichment, its efforts to build a heavy water reactor (which could be a source of plutonium, another way of getting a nuclear bomb) and any missile development that could deliver a nuclear weapon.
The Security Council has demanded that Iran suspend its enrichment activities while talks take place about its long-term plans.
Is Iran trying to build a nuclear weapon?
Iran says that it is not. It says it is simply exercising its right under an international treaty on nuclear weapons known as the Nuclear Non-Proliferation Treaty.
This bans it from developing a nuclear bomb but does allow it to develop nuclear power, including the technology needed to fuel power stations.
The UN's nuclear watchdog says it cannot "confirm the peaceful nature of Iran's nuclear programme".
Why should Iran not enrich as it sees fit?
Members of the Security Council, especially the United States, Britain and France, do not trust Iran.
For 18 years, Iran hid its enrichment programme and the suspicion was that it was trying to develop bomb technology in secret.
Iran has been told that if it stops enrichment, it will be offered help with developing nuclear power stations (including an offer to provide it with the necessary enriched uranium fuel).
However Iran has refused the Council's demand that it stop what it is doing before any talks take place.
Could there be a military attack on Iran?
The US says it wants a diplomatic solution. An attack on Iran would be hard to carry out and hard to justify legally.
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The US is said to have plans but it has plans for many contingencies and it has not taken a decision.
Some Israeli strategists say a nuclear-armed Iran would pose an unacceptable threat to their country, but it is thought unlikely that Israel would attack Iran without US support.