Washington, Jan. 11: President George W. Bush deflected a secret request by Israel last year for specialised bunker-busting bombs it wanted for an attack on Iran’s main nuclear complex and told the Israelis that he had authorised new covert action intended to sabotage Iran’s suspected effort to develop nuclear weapons, according to senior American and foreign officials.

White House officials never conclusively determined whether Israel had decided to go ahead with the strike before the US protested, or whether Israeli Prime Minister Ehud Olmert was trying to goad the White House into more decisive action before Bush left office.

But the Bush administration was alarmed by an Israeli request to fly over Iraq to reach Iran’s major nuclear complex at Natanz, where the country’s only known uranium enrichment plant is located.

The White House denied that request outright, American officials said, and the Israelis backed off their plans, at least temporarily. But the tense exchanges also prompted the White House to step up intelligence-sharing with Israel and brief Israeli officials on new American efforts to subtly sabotage Iran’s nuclear infrastructure.

This account of the expanded American covert programme and the Bush administration’s efforts to dissuade Israel from an aerial attack on Iran emerged in interviews over the past 15 months with current and former American officials, outside experts, international nuclear inspectors and European and Israeli officials.

The interviews also suggest that while Bush was extensively briefed on options for an overt American attack on Iran’s facilities, he never instructed the Pentagon to move beyond contingency planning.

The interviews also indicate that Bush was convinced by top administration officials, led by defence secretary Robert M. Gates, that any overt attack on Iran would probably prove ineffective, lead to the expulsion of international inspectors and drive Iran’s nuclear effort further out of view.

Bush and his aides also discussed the possibility that an airstrike could ignite a broad West Asia war in which America’s 140,000 troops in Iraq would inevitably become involved.

The covert American programme, started in early 2008, includes renewed American efforts to penetrate Iran’s nuclear supply chain abroad, along with new efforts, some of them experimental, to undermine electrical systems, computer systems and other networks on which Iran relies.

It is aimed at delaying the day that Iran can produce the weapons-grade fuel and designs it needs to produce a workable nuclear weapon.