Israel's opposition leader on Wednesday accused Prime Minister Benjamin Netanyahu of "meddling" in the US presidential election and harming Israel's ties with Washington in a dispute over Iran's nuclear programme.

The remarks by opposition leader Shaul Mofaz came as Netanyahu and the White House locked horns over how to handle Iran's nuclear programme, with Israel threatening unilateral military action against Tehran, despite American objections.

Mofaz said Netanyahu's pursuit of a very public dispute with President Barack Obama over Iran was an attempt to sway voters against the US leader, who faces a challenge from Republican rival Mitt Romney in the November ballot.

"Israeli meddling in internal US affairs and turning the US administration from an ally to 'an enemy' has caused us severe damage," Mofaz charged, at a session of the Israeli parliament, known as the Knesset.

"Please explain to us: who is Israel's greatest enemy -- the US or Iran? Who do you fear more -- (Iranian President Mahmoud) Ahmadinejad or Obama? Which regime is more important to overthrow -- the one in Washington, or in Tehran?" he asked.

"Explain to us, prime minister: what are your 'red lines' for handling the crisis with the United States?" he said in a spin on Netanyahu's repeated demands vis-a-vis Iran's nuclear programme, which Israel and much of the West believes is a drive for weapons.

Over the past 10 days, Netanyahu has repeatedly urged the international community to lay down "clear red lines" to Iran and make clear the consequences of crossing it, in what was widely interpreted as overt criticism of Washington.

"The United States is our greatest friend. It was before you and will be after you: the warm friendship doesn't depend on one president or another," Mofaz said.

"Don't sacrifice our relations with the United States on the altar of Iran's nuclear programme."

Israel has said a nuclear-armed Iran would pose an existential threat to the Jewish state and has wielded the threat of military action, but Washington backs continued diplomatic pressure and says it is not the time for a strike.

On Tuesday, Mofaz said he did not believe Israel would attack Iran this year.

"My assessment is that there won't be Israeli military action (against Iran) in 2012 for all sorts of reasons," he said at an academic college near Tel Aviv, his remarks reported in Wednesday's Yediot Aharonot daily.

"It is still not the time for it, there is no necessity, no international legitimacy and no national legitimacy.

"Israel's capabilities are very good, but they will not bring about a strategic change in Iran's nuclear programme, and will lead to a regional war in the Middle East," he said.

"I think the Netanyahu government and the prime minister himself are leading the campaign against Iran on every media platform for political reasons and for reasons of changing the agenda, and not for reasons of Israel's security.

"If they really intended to do something, this is not how one acts against a strategic threat to the State of Israel."