Iran, in a confidential letter posted Friday on an internal Web site of the U.N. nuclear monitor, said its fear of attack from the U.S. and Israel prompted its decision to withhold information from the agency.

In the letter, Iran said the U.N.'s International Atomic Energy Agency had repeatedly allowed confidential information crucial to the country's security to be leaked.

The IAEA, in response, urged Iran to reconsider, saying the decision would be in defiance of the monitor's 35-nation board. Both the Iranian document and the confidential IAEA response were made available to The Associated Press.

The exchange reflected heightened tensions between Iran and the Vienna-based IAEA arising from the country's refusal to heed the U.N. Security Council and freeze uranium enrichment and the council's decision earlier this week to increase sanctions in response to the Islamic republic's nuclear defiance.

The IAEA also is waiting for Iran to respond to its requests to install remote cameras at key locations at Iran's underground enrichment plant at Natanz.

No enrichment is yet taking place at Natanz, but diplomats accredited to the IAEA said Friday it may start within days. If so, those cameras are crucial for IAEA experts in their efforts to monitor possible attempts to reconfigure machinery there into making weapons grade uranium — used in the fissile core of nuclear warheads.

Iran insists it wants to enrich only to low levels, suitable for generating nuclear power. But the international community increasingly fears that the country may want to develop enrichment for weapons uses.

Iran said Sunday it would no longer provide the IAEA with advance notice about any new nuclear facilities planned — a decision the government spokesman Gholan Hossein Elham said came in response to the "illegal and bullying resolution by (the) Security Council."

Expanding on the decision, the confidential letter, dated March 29, declared that "the United States and the Israeli regime ... are threatening the use of force and attack against the Islamic Republic of Iran and have repeatedly stressed that military action is an option on the table.

"So long as such threats of military action persist, Iran has no option but (to) protect its security through all means possible, including protection of information which can facilitate openly stated and aggressive military objectives of the war mongers," said the letter, signed by Ali Ashgar Soltanieh, Iran's chief delegate to the IAEA.

Blaming the IAEA for failing "systematically and repeatedly to maintain confidentiality of sensitive information," Soltanieh wrote that "therefore such dangerous dissemination of sensitive information will have to be curtailed through steps which limit their scope and availability."

The agency, in response, noted in its Friday response that the move is "contrary to the board's decision and suggested it may indirectly be in breach of agreements linked to the Nonproliferation Treaty.

Calling Iran's decision "regrettable," the agency, in a letter signed by a deputy of senior IAEA official Vilmos Cserveny, urged the Iranian authorities "to reconsider their decision."

Iran had previously committed itself to informing the agency of any planned new nuclear construction before such construction begins — a commitment it has not always kept.

Former U.N. nuclear inspector David Albright said Iran's decision could allow for clandestine nuclear work related to its enrichment program.

Albright, whose his Washington-based Institute for Science and International Security tracks Iran's nuclear program, said that Iran may be looking to build a "backup facility" for enrichment that would remain undetected — and safe — in case of attack by the United States or Israel.