"Answering questions about their past nuclear activities is a step, but they still need to suspend their enrichment and reprocessing activity," said a White House spokesman accompanying President George W. Bush on a Middle East tour.

"Another declaration is no substitute for complying with the UN sanctions," said Gordon Johndroe.

The International Atomic Energy Agency (IAEA) said earlier Sunday that Iran has agreed to clear up remaining questions on its nuclear programme -- including any military activity -- in four weeks.

IAEA chief Mohamed ElBaradei and Iran's supreme leader Ayatollah Ali Khamenei and President Mahmoud Ahmadinejad agreed a "work plan" on ending the Iran nuclear standoff should be completed within that timeframe, it said.

Iran insists that it has an inalienable right to develop nuclear power for a growing population and adamantly refuses to suspend enrichment, in defiance of UN Security Council resolutions.

The key sticking point in the standoff is the demand of Western powers that Iran suspends uranium enrichment, a process they fear Tehran could use to make a nuclear weapon. Iran refuses to obey, insisting its drive is peaceful.

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