Iran has scoffed at the idea of US military action to halt its nuclear programme and offered no hint of compromise to end the impasse.
On Thursday, the Iranian defence minister said Tehran was ready for any eventuality.
"The United States has been threatening Iran for 27 years and this is not new for us. Therefore we are never afraid of US threats," Mostafa Mohammad Najjar told reporters.
"If you take into account the fact that they are not doing anything, this shows it is just talk," he said.
Najjar said Iran was ready to negotiate, but would deal with any challenge confronting it.
George Bush, the US president, has vowed to stop Iran from getting atomic weapons and has refused to rule out military options, including nuclear strikes, if diplomacy fails.
Senior IAEA inspectors were due in Iran on Friday to gauge Iranian compliance for the report that Mohamed ElBaradei, the UN watchdog's director, is preparing for the Security Council.
Pressing for sanctions
The United States, Britain and France want the Security Council to approve targeted sanctions on Iran, such as travel bans and asset freezes, if it refuses to back down.
But China and Russia, the council's other two veto-holders, doubt punitive measures will work. Big-power talks in Moscow this week failed to produce a consensus on future action.
European diplomats on Thursday dismissed as unacceptable a suggestion that Iran take a brief "technical pause" from nuclear enrichment to revive collapsed negotiations with the EU.
"A full suspension is the only way to resolve this and the Iranians have given no indication they are willing to do that," a senior EU diplomat told Reuters.
Condoleezza Rice, the US secretary of state, said on Wednesday that the world was mobilised to deny Iran nuclear weapons.
"We are prepared to use measures at our disposal - political, economic, others, to dissuade Iran," she said.
Russia on Thursday rejected a call from the United States, which has long maintained its own trade embargo on Iran, to halt work on the Islamic Republic's Bushehr nuclear power station.
Russia's state atomic energy agency is contracted to help Iran build the $1 billion reactor. A senior US official said on Wednesday that a Russian withdrawal would help persuade Iran to abandon its separate uranium enrichment programme.
"The United States has been threatening Iran for 27 years and this is not new for us. Therefore we are never afraid of US threats"
Mostafa Mohammad Najjar, Iranian defence minister
"Every country has the right to decide for itself with whom and in what way it cooperates with other states," Mikhail Kamynin, a Russian foreign ministry spokesman said, adding that only the UN Security Council could override this principle.
Speaking in Moscow, Nicholas Burns, the US undersecretary of state, had also repeated Washington's view that Moscow should cancel the planned sale to Iran of Tor tactical surface-to-air missiles. Moscow and Tehran say they are for defensive purposes.
Kamynin's statement did not mention the missile sales.
Iranian nuclear negotiators were in Moscow on Thursday but there was no word on what they were doing. They met officials of Britain, France and Germany late on Wednesday, but a British diplomat said there had been no breakthrough.