International Atomic Energy Agency (IAEA) Director General Mohamed ElBaradei, speaking in the wake of allegations that UN chief Kofi Annan was bugged by Britain, called the practice a violation of basic human rights.
"We haven't come across any evidence that we have been bugged but we work on the assumption that we have been bugged all the time," he told reporters during a visit to Brussels.
"We take whatever measures necessary, we try to clean up... to make sure that there is no bugging device," said the head of the Vienna-based UN agency, which is in charge of monitoring nuclear safety worldwide.
But he said: It's unfortunate but this is part of the rules of the game," adding: "It's a pity.... It's a violation of a basic human right which is (the) right to privacy."
The IAEA has most recently been involved in high-profile monitoring of nuclear facilities in Iran. The United States notably insists that Tehran is still trying to develop nuclear weapons.
Former British minister Clare Short last week alleged that British intelligence agents had eavesdropped on Annan's conversations and that she had seen the transcripts.