JERUSALEM: Israel and the United States have agreed to postpone a major military defence exercise scheduled for spring, Israeli public radio reported Sunday, amid rising regional tension over Iran's nuclear programme.

The exercise, codenamed "Austere Challenge 12," would be pushed back to the end of 2012 because of unspecified budgetary concerns, the radio said, citing military sources.

An Israeli Defence Ministry source, who spoke on condition of anonymity, told AFP said the delay had not been finalised.

"No final decision has been made yet, discussions with our American counterparts are ongoing," he said.

But Israel's army radio, citing a defence official, said the drill was being postponed to avoid "unnecessary headlines in such a tense period."

The joint manoeuvre was to have been the biggest yet between the two allies, and was seen as an opportunity for the two sides to display their joint military strength at a time of growing concern about Tehran's nuclear ambitions.

Israel, the United States and much of the international community accuse Iran of using its nuclear programme to mask a weapons drive, a charge denied by Tehran.

The postponement appeared to suggest fears that the exercise could dangerously further ramp up regional tensions, at a time when Iran has already threatened to close the strategic Strait of Hormuz.

The Israeli army insisted last month that the manoeuvres were planned in advance and denied they were related to Iran.

"The exercise scenario involves notional, simulated events as well as some field training and is not in response to any real-world event," the military said in a written response to an AFP query.

"These exercises, which are part of a long-standing strategic partnership, are planned in advance and part of a routine training cycle designed to improve the inter-operability of our defence systems."

The postponement was not expected to affect a visit to Israel by top U.S. military chief General Martin Dempsey, who is scheduled to arrive later this week and meet with Israel's Defence Minister Ehud Barak and Chief of Staff Benny Gantz.

But the delay was announced as reports suggested unease in U.S.-Israeli relations over the best response to Iran's nuclear programme, and after an Israeli official voiced "disappointment" at Washington's approach.

The United States has spearheaded a push for international sanctions against Iran, including on its oil exports and financial institutions.

But Israel's Strategic Affairs Minister Moshe Yaalon told Israeli public radio that he thought US President Barack Obama's administration should be tougher.

"France and Britain understand that the sanctions must be strengthened, in particular against the Iranian Central Bank," Yaalon said.

"The U.S. Senate is also in favour, but the U.S. government is hesitating, fearing higher oil prices in an election year," Yaalon said. "It's disappointing."

Israel's deputy foreign minister Danny Ayalon, speaking Sunday ahead of a trip to Britain expected to include discussions on Iran, also accused the international community of dragging its feet.

"It is regrettable that the international community has not yet used all the means at its disposal to stop the Iranian nuclear programme," he told public radio.

Israel has made no secret of its desire to see crippling sanctions imposed on Iran in a bid to slow its nuclear development, and reports suggest the Jewish state has also taken other actions to retard the programme.

The Jewish state is suspected of involvement both in a computer worm that reportedly set back Iran's nuclear efforts, as well as a campaign of assassinations of Iranian nuclear scientists.

Israel has been tight-lipped about its involvement in operations targeting the programme, but reports in Time and Foreign Policy magazine in recent days both pointed the finger at Israel's intelligence agency Mossad.

Foreign Policy reported that Israel's actions had created friction with Washington, and the Wall Street Journal said Friday that U.S. officials had warned the Jewish state against unilateral military action against Iran.

The newspaper said Washington had prepared contingency plans to protect U.S. assets in the region in case Israel went ahead with a military strike anyway.

Yaalon said Sunday that a military strike remained a last resort for Israel.

"Israel must defend itself. I hope that we will not arrive at that point," he said.