Iran is blaming the US and Israel for its decision to withhold information from the outside world on its nuclear program, saying in a confidential letter that threats from the two "warmongers" led it to curtail cooperation with the International Atomic Energy Agency. The IAEA - the UN nuclear 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. Both the Iranian document and the confidential IAEA response were made available to The Associated Press on Friday. The exchange reflected heightened tension between Iran and the Vienna-based IAEA arising from Teheran's refusal to heed the UN 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 UN body's involvement in trying to curb Teheran's nuclear defiance The agency also is waiting for Teheran to respond to its requests and allow it 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 that Teheran may start doing so 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 Teheran may want to develop enrichment for weapons uses. Its resistance to having the cameras mounted in locations the agency has specified is further raising concerns. A diplomat accredited to the agency said the centrifuges are in the lowest level of the three-tiered Natanz facility and are blocked from view by a wall. The agency has only been able to mount cameras outside that wall, he said, demanding anonymity because his information was confidential. The agency's request for extra cameras was made by Olli Heinonen, the IAEA deputy director general of the Iran file. It was unclear whether Heinonen's move was prompted by concerns that Iran was approaching the limit of 500 centrifuges assembled in series - a number that the IAEA considers the red line as far as additional monitoring is concerned. Two diplomats on Friday said that Iran had already linked up more than 900 of the devices and was ready to introduce uranium gas in them, starting the process of enrichment on a larger scale than previous attempts. A third said negotiations over the IAEA request for additional cameras were scheduled for the weekend between senior Iranian and agency officials. Iran initially announced its move to keep some information from the agency on Sunday, with officials saying they would no longer provide the IAEA with advance notice about any new nuclear facilities they wanted to build. The decision was in response to the "illegal and bullying resolution by (the) Security Council," said government spokesman Gholan Hossein Elham. 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 warmongers," 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." Before the decision, Teheran had committed itself to informing the agency of any planned new nuclear construction before such construction begins - a commitment it has not always kept. For instance, Teheran delayed informing the agency three years ago that it was building tunnels in the central city of Isfahan to house parts of its uranium enrichment program. Former UN nuclear inspector David Albright said Iran's decision could clear the path for Iran to do clandestine nuclear work related to its enrichment program - a possible pathway to nuclear arms. Albright, whose 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.