Iran has been accused of concealing a second uranium enrichment plant in defiance of international calls for transparency over its nuclear plans.
The leaders of the US, UK and France demanded UN inspectors be given immediate access to the facility.
Iran revealed the existence of the plant to the UN watchdog on Monday, saying it was not yet operational and would only be used for nuclear energy.
Tehran has previously acknowledged it has one enrichment plant, at Natanz.
Iran's decision to build a secret facility represented a "direct challenge to the basic compact" of the global non-proliferation regime, US President Barack Obama said, making a statement in Pittsburgh, where he is hosting a G20 summit.
Despite Iran's assertions that the facility was for peaceful purposes, the new plant was "not consistent" with that goal, the US president said.
Speaking alongside UK Prime Minister Gordon Brown and French President Nicolas Sarkozy, Mr Obama said it was time for Iran to begin meeting its international commitments.
BBC NEWS | Middle East | Iran 'concealed nuclear facility'