Pittsburgh/Vienna, Sep 25 (DPA) Hours after it was confirmed that Iran has a second, previously unknown, nuclear enrichment plant, US President Barack Obama Friday said the size of the new plant was 'inconsistent' with Iranian claims that it was being used to produce civilian nuclear power.

Speaking at the G20 summit and standing alongside British Prime Minister Gordon Brown and French President Nicolas Sarkozy, Obama said the 'disturbing' news of the second facility demonstrates Tehran's willingness to deceive the world and violate international norms.

The International Atomic Energy Agency (IAEA) confirmed Friday that Iran disclosed in a letter on Monday about the existence of the plant, which had been kept secret for years.

'The existence of this facility underscores Iran's continued unwillingness to meet its obligations under UN Security Council resolutions,' Obama said.

'It is time for Iran to act immediately to restore the confidence of the international community by fulfilling its international obligations,' he added.

Sarkozy said that Iran must come clean about its nuclear activities by December or face a new round of international sanctions.

'We cannot let the Iranian leaders gain time while the motors are running,' Sarkozy said.

Brown endorsed calls for more sanctions if Iran does not soon come into compliance.

'Iran's nuclear programme is the most urgent proliferation challenge the world faces today,' Brown said.

Iranian President Mahmoud Ahmadinejad maintains that Iran's nuclear ambitions are limited to generating energy.