Iran in January and February denied International Atomic Energy Agency (IAEA) inspectors access to the Parchin military site where explosives testing for warhead research allegedly took place.

During talks Thursday at the IAEA in Vienna, the United States, Russia, China, Britain, France and Germany issued a statement urging Iran to "fulfill its undertaking to grant access to Parchin."

US State Department spokeswoman Victoria Nuland said the statement contained an expectation that "the IAEA will be able to get into Parchin soon, as well as all the other facilities that it wants to see."

But Nuland added: "There's not an expectation that that has to happen before talks start, although it should have already happened."

Iran says the IAEA already visited Parchin near Tehran in 2005 and that it is under no obligation to allow access because the site is non-nuclear.

Iran is highly sensitive about allowing access to military sites following a large explosion at the Bid Ganeh base in November and multiple assassinations of nuclear scientists it has blamed on Israel and the United States.

The European Union (EU) on Tuesday announced that the six world powers would resume talks with Iran on its controversial nuclear program, following a hiatus of more than a year, but a time and venue have still to be set.

In a February 14 letter to the EU, Iran said it was ready to resume the deadlocked negotiations at the "earliest" opportunity as long as the world powers respected its right to peaceful atomic energy.

At the last talks between the two sides held in Istanbul in January 2011, Iran refused to address questions on its nuclear program, laying down what diplomatic sources said were "pre-conditions" such as a lifting of sanctions.

The United States and other Western powers charge that Iran's uranium enrichment program masks a drive to produce nuclear bombs. Iran denies the charge, insisting its program is purely for peaceful purposes.

Citing unnamed Western diplomats and intelligence sources, the report said that during Prime Minister Benjamin Netanyahu's visit to Washington this week, the US administration offered to supply Israel with advanced bunker-busting bombs and long-range refuelling planes.

In return, Israel would agree to put off a possible attack on Iran till 2013, after the US elections in November.

Israel and much of the international community fear Iran's nuclear programme masks a weapons drive, a charge Tehran denies, and it was top of the agenda at talks between Netanyahu and US President Barack Obama in Washington this week.

The United States and Israel are at odds over just how immediate the Iranian threat is. Netanyahu said on Monday that sanctions against Iran have not worked, and "none of us can afford to wait much longer."

A key difference between Washington and Israel has emerged on the timeline available for a military strike against Iran, with the Jewish state warning that the weaponry available to it gives it a shorter window for action.

In response, the report said, the US administration offered to give Israel weapons and material that could extend its window to act against Iran.

In particular, it would offer bunker-busting bombs more powerful than those currently possessed by Israel, which would allow the Jewish state to target Iranian facilities even under solid rock.

Earlier this week, the Ynet website reported said that Israel Military Industries (IMI), one of the country's leading weapons manufacturers, had upgraded its MPR-500 guided missiles, turning them into "bunker busters" capable of penetrating double-reinforced concrete walls and floors 200mm thick.

But figures from a poll published on Thursday showed that almost six out of 10 Israelis -- or 58 percent -- were against the idea of a pre-emptive strike on Iran's nuclear facilities without US backing.

The same poll, published by Haaretz newspaper, also found that over half of the respondents trusted Netanyahu and Defence Minister Ehud Barak to handle the Iran issue.

The Maariv report comes shortly after world powers known as the P5+1 -- five UN Security Council members plus Germany -- offered to resume long-stalled talks with Tehran over its contested nuclear programme.

Israel has cautiously welcomed the talks, but warned it must be prepared for the potential failure of any new dialogue with Iran.