An ill-advised Israeli attack on Iran would be less likely if Mitt Romney became the next president because he would shore up strained US relations with Israel, an advisor said Thursday.

If the Republican nominee wins the race for the White House, he would tighten sanctions against Iran over its nuclear program and bolster ties with Israel, which have deteriorated under President Barack Obama's administration, said Dov Zakheim, a foreign policy adviser to the candidate.

"If you don't want the Israelis to go off half-cocked, and I don't think there's anybody in the American national security community that does, the way to do it is not to create daylight between us and the Israelis," Zakheim told a group of defense reporters.

"The way to do it is to win their confidence," said Zakheim, who served as a senior Pentagon official during former president George W. Bush's first term and under Ronald Reagan's administration in the 1980s.

If Israeli Prime Minister Benjamin Netanyahu retains his post after elections next year, and if Obama wins a second term in the White House, the Israeli leader might be more inclined to take unilateral military action due to the tense relationship with Washington, Zakheim said.

"What Mr Romney says he's going to do is win Israeli confidence, close the loopholes in the sanctions and really make it much more realistic that we will not have to attack Iran and nor will the Israelis," he said.

He said that Obama had mismanaged relations with Israel and "that's why the polls in Israel consistently show Mr Obama as being the most unpopular American president that Israelis have ever identified."

Romney's adviser also criticized the Obama administration for making exceptions for the sanctions on Iran for certain countries heavily dependent on foreign oil, including China.

"And you still have 20 countries that somehow are being let off the hook on these sanctions," he said.

The move sent a signal of weakness, he said, adding: "What do you think the Iranians think when that happens?"

Romney would seek an understanding with Israel on defining a "red line" on Iran policy that would trigger potential military action over Tehran's nuclear project, he said.

But he said the Obama team was asking Israel to trust US intelligence reporting, which he suggested was unreliable.

"So what we are essentially doing is saying to the Israelis: 'Trust us, we will in fact know when the Iranians are ready to get their bomb.'"

Referring to last month's deadly attack on a US consulate in Libya, he said it was "the same intelligence community that didn't seem to know ... what was going to happen in Benghazi, that didn't seem to know about the Arab Spring."