Iran is blaming the U.S. and Israel for its decision to withhold information from the outside world on its nuclear program, saying in a confidential letter obtained Friday that their alleged war mongering led it to curtail cooperation with the International Atomic Energy Agency.

The International Atomic Energy Agency - the UN monitor - in turn told Iran that it is defying the 35-nation board of the agency with its move and urged it to reverse its decision.

The exchange reflected heightened tension between Iran and the Vienna-based IAEA arising from Tehran's refusal to heed the U.N. Security Council and freeze uranium enrichment and the council's decision earlier this week to pass a second resolution increasing sanctions in response to the Islamic republic's nuclear defiance. A decision by the IAEA board to refer Iran to the council last year led to that U.N. body's involvement in trying to curb Tehran's nuclear defiance.