The White House reiterated its support for a term limit for UN organisation chiefs that would require the 62-year-old Egyptian diplomat to step down as head the agency when his second term expires next year.

“The United States government has always supported the policy that heads of UN organisations should stay no more than two terms,” said White House spokeswoman Suzy DeFrancis.

She was responding to a Washington Post report that US officials were combing through intercepted phone conversations between Mr ElBaradei and Iranian diplomats for evidence that could be used to force him to leave.

Ms DeFrancis refused to respond to accusations of eavesdropping, saying she could not comment on intelligence matters.

Mr ElBaradei, who has run the UN watchdog agency since 1997, angered members of the Bush administration by questioning US intelligence on Iraq and later by adopting a cautious approach to Iran’s nuclear program.

He was appointed to a second term in September 2001 and has been asked to stay on for a third term by members of the IAEA board.

Experts said the Bush administration has been pressing for Mr ElBaradei to observe the two-term limit for months and now appears to be intensifying pressure to oust him.

“The two-term argument has not worked, and there appears to me to be an effort by someone in the administration to pursue another route,” said Daryl Kimball, executive director of the Arms Control Association, a private Washington-based arms control policy group.

The Washington Post report, quoting three unnamed US government officials, said the intercepted phone conversations had produced no evidence of nefarious conduct by Mr ElBaradei.

But it said some within the administration believe the conversations show Mr ElBaradei lacks impartiality because he tried to help Iran to navigate a diplomatic crisis over its nuclear programs.

The newspaper said the United States had been canvassing for possible candidates to replace Mr ElBaradei, but had yet to settle on one ahead of a December 31 deadline.

Washington’s top favorite to replace ElBaradei is Australian Foreign Minister Alexander Downer, but he has been unwilling to challenge the IAEA chief, the Post said.

“Our original strategy was to get Alex Downer to throw his hat in the ring, but we couldn’t,” a US policy maker told the Washington Post.