US President George W. Bush last year rejected a secret Israeli request for an air strike against the main Iranian nuclear complex using US bunker-busting bombs, The New York Times reported on its website late Saturday.

But citing unnamed senior US and foreign officials, the newspaper said Bush had authorized a new covert operation aimed at sabotaging Iran's suspected effort to develop nuclear weapons.

The request was made last year by Israeli Prime Minister Ehud Olmert, who wanted US bunker-busting bombs and permission to fly over Iraq to attack Iran's major uranium enrichment complex at Natanz, the report said.

But top US administration officials led by Defense Secretary Robert Gates had convinced Bush that any overt attack on Iran would prove ineffective, lead to the expulsion of international inspectors and drive Iran's nuclear program deeper underground, the paper said.

Bush and his aides also discussed the possibility that an airstrike could ignite a broad Middle East war in which US troops in Iraq would inevitably become involved, according to The Times.

However, Bush opted for more intensive covert operations actions aimed at Iran, the report said.

They include renewed US efforts to penetrate Iran's nuclear supply chain abroad, undermine the country's electrical and computer systems as well as other networks on which Iran relies, The Times said.

The effort is aimed at delaying the day that Iran can produce weapons-grade fuel for a workable nuclear weapon, according to the report.