From BBC News:
Iran insists its nuclear sites are engaged in non-military work
Russia has ruled out supporting fresh sanctions against Iran, despite a UN report that says Tehran may be trying to develop nuclear weapons.
Deputy Foreign Minister Gennady Gatilov told Interfax news agency that extra sanctions could be interpreted as a means of regime change in Iran.
Earlier, France and the US both said they would pursue new sanctions against Iran in the wake of the IAEA report.
Iran insists that its nuclear programme is for peaceful means.
However, the US and its allies have long suspected that Iran is developing nuclear weapons, which it is feared could threaten Israel.
"Any additional sanctions against Iran will be seen in the international community as an instrument for regime change in Iran," Mr Gatilov said.
"That approach is unacceptable to us, and the Russian side does not intend to consider such proposals."
The International Atomic Energy Agency said it had information indicating Iran had carried out tests "relevant to the development of a nuclear explosive device".
The IAEA report - published on the Institute for Science and International Security website - says the research includes computer models that could only be used to develop a nuclear bomb trigger.
It documents alleged Iranian work on the kind of implosion device that would be needed to detonate a nuclear weapon.
On Wednesday, a defiant Iranian President Mahmoud Ahmadinejad said his country will not budge "one iota" from its nuclear programme.
He said the IAEA report was based on "empty claims" provided by the US.
"Why do you damage the [UN] agency's dignity because of America's invalid claims?" he said in a televised speech.
Addressing the US he added: "We will not build two bombs in the face of your 20,000. We will develop something that you cannot respond to, which is ethics, humanity, solidarity and justice.
"You should know that no enemy of the Iranian people has ever tasted victory."
French Foreign Minister Alain Juppe said the seriousness of the report warranted a meeting of the UN Security Council.
"If Iran refuses to conform to the demands of the international community and refuses any serious co-operation, we stand ready to adopt, with other willing countries, sanctions on an unprecedented scale," he told French radio.
Mr Juppe said tough sanctions were needed to "prevent Iran from continuing to obtain resources that allow it to pursue its activities in violation of all international rules".
A senior US official said Washington would consult with partners on "additional" pressure and sanctions on Tehran.
"We don't take anything off the table when we look at sanctions. We believe there is a broad spectrum of action we could take," the official said, quoted by AFP news agency.
The EU said the report "seriously aggravates" existing concerns.
"Overall these findings strongly indicate the existence of a fully-fledged nuclear weapons development programme in Iran," said a spokeswoman for EU foreign policy chief Catherine Ashton.
Baroness Ashton represents six world powers - the UK, China, France, Germany, Russia and the US - in stalled negotiations with Iran over its uranium enrichment programme.
The BBC's Kim Ghattas in Washington says China is also unlikely to support further sanctions against Iran.
Last Sunday Israeli President Shimon Peres said a military strike on Iran was becoming more likely.
"There is an impression that Iran is getting closer to nuclear weapons," he told the Israel Hayom daily.
- How an implosion device could trigger a nuclear bomb
- Cross section of implosion device
- 1. Detonators triggered
- 2. Explosives create shock- waves and compress core
- 3. Initiator kick-starts the fission process
- 4. Compressed fissile core (of uranium or plutonium) becomes unstable and starts nuclear chain reaction
- 5. Tamper layer contains neutrons and expansion briefly, to maximise fission