Long-strained ties between Benjamin Netanyahu and Barack Obama sprang to the fore of Israel's election campaign on Wednesday after the US president was quoted as criticizing the prime minister's character.

Less than a week before a Jan. 22 ballot that opinion polls predict the right-wing Netanyahu will win easily, Israeli media highlighted a US commentator's column on Obama and questioned whether the Democratic president was trying to sway the vote.

Netanyahu's office declined comment on Tuesday's unsourced column by Bloomberg's Jeffrey Goldberg, which described Obama as frustrated at West Bank settlement building that has deepened Israel's diplomatic impasse with the Palestinians.

"If Reuters can confirm that the story is true, I'll talk about it," said Netanyahu spokesman Mark Regev.

The White House has not commented on the column's content.

"Obama said privately and repeatedly, 'Israel doesn't know what its own best interests are'," Goldberg wrote.

The president "seems to view the prime minister as a political coward, an essentially unchallenged leader who nevertheless is unwilling to lead or spend political capital to advance the cause of compromise", added Goldberg.

Some Israeli commentators saw the column as payback for Netanyahu's perceived back-room lobbying on behalf of Republican Mitt Romney in his failed run against Obama in November's U.S. election. Netanyahu has denied any such meddling.

Though it was front-page news, the Bloomberg column looked unlikely to dent Netanyahu's electoral lead, with his Likud-Beiteinu list expected to take around 34 of parliament's 120 seats and form the next coalition government.

A centrist challenger, former Foreign Minister and peace negotiator Tzipi Livni, has made Israel's international isolation under Netanyahu the focus of her campaign. She has lagged in polls with a projected 6 to 8 parliamentary seats.

"Attempts to speak to the Israeli voter through the American press are total non-starters," said Amotz Asa-El, a fellow with the Hartman Institute, a liberal think-tank in Jerusalem.

Most Israelis, Asa-El argued, were disenchanted by abortive peacemaking, worried by regional upheaval and preoccupied with domestic affairs. Foreign criticism of Netanyahu, he said, could shore him up against rivals further to the right.

"These (far-rightists) have never heard of Bloomberg, let alone of Jeffrey Goldberg. If anything, this (criticism) is likely to make them vote for Netanyahu," Asa-El said. "There is no traffic of undecided voters between the rightist bloc and the center-left bloc, only within the blocs."

Several Israeli officials questioned whether the quotes attributed to Obama reflected the view of his administration, which, like the Netanyahu government, has played up the strength of bilateral ties on issues ranging from the Palestinians to the Syrian insurgency and Iran's disputed nuclear program.

Vice Israeli Premier Silvan Shalom, of the Likud, told Israel's Army Radio: "I don't know if these things were said, because he (Obama) did not say them in his own voice."

Shalom appeared to acknowledge tensions between Netanyahu and Obama. But he praised the US president's tack on Iran - Israel's main regional worry - and said bilateral ties trumped personal "baggage".

"I have seen many countries where the relationship between the leaders was good but there were no common interests and thus no cooperation. By contrast, in other places where there were interests but, perhaps, the relationships were less good, the interests were ultimately what took precedent," Shalom said.