JERUSALEM: The United States' top military officer arrived in Israel on Thursday as the allies coordinated efforts to curb Iran's nuclear program - and play down suggestions they are at odds on strategy.

The United States, which is leading Western pressure on Tehran to curb controversial uranium enrichment, has voiced concern that the Israelis could attack their foe preemptively and deepen instability in an already volatile region.

This week's postponement of joint military manoeuvres - and sharp remarks in Washington disowning the killing of an Iranian nuclear scientist which many suspect was the work of Israeli agents - have fuelled speculation that General Martin Dempsey, chairman of the Joint Chiefs of Staff, may have flown in from Europe to lay down the law and rein in his close ally.

Officials on both sides rejected that idea: "Chiefs of staff deal with preparing their militaries for various options," Israeli Defence Minister Ehud Barak said on Wednesday. "They don't deal in passing diplomatic messages."

Barak also said that any decision about an Israeli attack on Iran was "very far off". Like the United States, Israel does not believe Iranian assurances that its nuclear research has no military purpose. It says it would use force to prevent the Islamic Republic from acquiring atomic weapons that Israel believes would threaten the survival of the Jewish state.

Along with an unusually dovish comment last week by Prime Minister Benjamin Netanyahu that U.S.-led economic sanctions against Iran appeared to be having an effect, Barak's remarks appeared designed to counter suggestions that Israel was losing patience with U.S. President Barack Obama's diplomatic approach.

Both sides also insisted that they postponed a joint air defence exercise, planned for May, for operational reasons that were entirely unrelated to the situation with Iran.

FRICTION

A record of barely concealed friction between Netanyahu's right-wing coalition and the Democrat in the White House has added to speculation about differences over Iran - differences which are now particularly sensitive as Obama campaigns for re-election in November and faces criticism from some U.S. voters for lacking vigour in his support for Israel.

Barak further played down the importance of Dempsey's first visit to Israel in his current capacity by noting that, as Israeli defence minister, he was in regular direct contact with his U.S. counterpart, Defense Secretary Leon Panetta.

"The dialogue between us is conducted on the basis of mutual respect," Barak said. "This administration gives unprecedented support to Israel's defence establishment."

A U.S. official said Dempsey would be "meeting with counterparts and important close allies, regardless of any current political situations". He will leave on Friday as Israel shuts down for the Jewish sabbath.

Alon Ben-David, military affairs analyst for Israel's Channel 10 television, said he expected Dempsey to emphasize that both allies see a threat in a nuclear-armed Iran, but there is no need for rushed or drastic action.

"He will explain to the Israelis, in a delicate way, just how much the United States sees a risk in an Israeli action against Iran," Ben-David said.

Iran denies seeking the bomb, but its secretive nuclear projects and advances in ballistic missile development have drawn international censure and sanctions. The U.S. navy has also manoeuvred in the Gulf in the face of an Iranian threat to blockade the Strait of Hormuz, a strategic oil-export channel.

Israel, which is presumed to have the only nuclear arsenal in the Middle East, has urged Washington to stiffen penalties on Iran's energy sector and central bank, and hinted it could resort to unilateral attacks if it deems diplomacy a dead end.

Obama's Republican opponents have seized on such differences between the allies ahead of this year's presidential election. The incumbent says he is determined to rein in Iran and has sought to burnish his pro-Israel credentials.

A senior Israeli official played down the unilateral Israeli "military option" on Thursday and appealed to U.S. interests in a Middle East where the popular Arab uprisings have shaken U.S.-aligned leaders, some of whom, like those in the Gulf, share Israeli and Western views of Iran as a threat.

"America is, to my regret, perceived in the Arab world as a country that has become weak and may be unable to provide them with the protection they desire in the face of Iran," Deputy Prime Minister Dan Meridor told Army Radio.

Should the Obama administration succeed in changing such perceptions among its Arab allies, Meridor said, it "would shore up their status, which is so important -- important for them and, by the way, for us -- in the Arab world".