Israeli critics are warning that Prime Minister Benjamin Netanyahu has gone too far in what they call his "meddling" in favour of Republican candidate Mitt Romney in the US presidential campaign.

"Will Barack Obama punish Israel, if he is reelected on November 6," the Yediot Aharonot daily asked.

Like other media, the top-selling tabloid says that Netanyahu has become "Obama's opponent" and has broken a taboo by seeking to weaken the incumbent Democrat, rather than observing neutrality.

Netanyahu "interfered, grossly, vulgarly and unreservedly in the campaign" accused the left-leaning daily Haaretz.

"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," opposition leader Shaul Mofaz taunted Netanyahu in a parliamentary debate last week.

"That's nonsense," Netanyahu told Israeli media, in interview published ahead of this week's Rosh Hashana Jewish New Year holiday, saying he would continue to demand the United States set clear "red lines" that Iran would not be permitted to cross in its nuclear programme.

Obama does not want to lock the US into such an ultimatum and says there is still time for diplomacy and international sanctions to quash what he and Israel say are Iran's nuclear arms plans.

Netanyahu says time is fast running out and has warned of a unilateral Israeli strike against Iranian nuclear sites, despite opposition from friendly countries such as the United States, Germany, Britain or France.

"The issue that guides me is not the elections in the United States but the centrifuges in Iran," he has said.

Defence Minister Ehud Barak is distancing himself from such public washing of dirty linen, saying that such "differences" should be confined to closed-door meetings.

-- 'Bibi the American' --

For most analysts, beyond his bellicose rhetoric, Netanyahu, known to friend and foe alike by his nickname "Bibi", wants to wring as many concessions as possible from Obama before the election, hoping to play on Israel's support among Jewish, and many conservative Christian, voters.

Any loss of the traditionally Democratic Jewish vote could be crucial if the race is as close as that when George W. Bush won by a wafer-thin margin in 2000 against the Democrat Al Gore.

Romney -- who was warmly received by Netanyahu in Jerusalem in late July -- bluntly accused his rival of having "abandoned" Israel against Iran.

Netanyahu prides himself on an intimate knowledge and understanding of the United States, where he lived for many years. He is surrounded by advisers sharing his pro-Republican sentiments.

One of those closest to him is Jewish American billionaire Sheldon Adelson, owner of the pro-Netanyahu Israel Hayom daily and a major contributor to Romney's campaign.

There has never been chemistry between Bibi and Obama.

In May 2011, in front of TV cameras in the Oval Office Netanyahu gave his host a very public putdown, rejecting his proposal to base the borders of a future Palestinian state on the 1967 lines, then lecturing him on the historic struggles of the Jewish people.

According to Yediot Aharonot, it is for this reason -- not because of differences over Iran -- that Netanyahu is betting on Romney.

"If he wins, it will be months before he puts his administration in place," commentator Nahum Barnea writes in the paper. "On the other hand, if Obama wins a second term he could as a matter of course demand very significant concessions (from Israel) on the dispute with the Palestinians."

"Obama has tried and failed (to revive the peace process) but he is surrounded by advisers who are convinced that he must try," Barnea concludes.