The New York Times reports Tehran may be planning to build more uranium enrichment sites, defying international demands.
The paper quotes anonymous sources from several governments and international agencies as backing the claims.
The Times reports UN inspectors are looking for evidence of two such sites.
The U.S. daily says inspectors were tipped off by an interview given by Ali Akbar Salehi, head of Iran's Atomic Energy Organization, who told the Iranian Student News Agency that construction could start on two new enrichment sites after Iranian New Year on March 21.
The UN Security Council has passed three rounds of sanctions against Iran for its failure to halt its uranium enrichment program.
Now, the United States, France and Britain are pushing Russia and China to back a new round of United Nations sanctions against Iran, which they suspect is developing nuclear weapons.
The issue will be at the top of the agenda of foreign ministers from the G8 countries - US, Canada, Britain, France, Italy, Japan, Germany and Russia - in the Canadian capital, Ottawa, this week.
compiled from agency reports