Pittsburgh, Sep 25 - The US, Britain and France Friday charged Iran with defying the UN Security Council and warned of sanctions if Tehran refuses the International Atomic Energy Agency to access a new uranium enrichment facility.

'This site deepens a growing concern that Iran is refusing to live up to those international responsibilities, including specifically revealing all nuclear-related activities,' President Barack Obama said.

'To put it simply: Iran must comply with UN Security Council resolutions and make clear it is willing to meet its responsibilities as a member of the community of nations,' he said, with French President Nicolas Sarkozy and British Prime Minister Gordon Brown by his aide.

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

The issue has taken centrestage here, where leaders of 19 countries, including Prime Minister Manmohan Singh, and the EU have converged for the G20 Summit to take stock of the year-long global financial crisis and how to deal with that.

Sarkozy said Iran first built an enriching plant of Natanz in 2002 and has now set up another at Qom over the past several years in violation of resolutions from the Security Council.

'If by December there is not an in-depth change by the Iranian leaders, sanctions will have to be taken.