Whatever the outcome, Iran's presidential vote will not ease tensions with Israel as Tehran is unlikely to halt its nuclear drive or tone down its rhetoric against the Jewish state, Israeli analysts say.

Iran's hard-fought election on Friday comes at a key moment after US President Barack Obama broke away from his predecessor's approach by offering direct dialogue with Tehran to try to end the standoff over its nuclear drive.

But Israeli analysts said even the election of a moderate president would not bring major change, as Iran's strategic policies are ultimately decided by supreme leader Ayatollah Ali Khamenei.

"The key decisions in the nuclear field are taken by the spiritual leader Khamenei, so it doesn't matter who is elected president," said Dore Gold, president of the Jerusalem Centre for Public Affairs research group.

"All of the candidates support continuing the nuclear programme," said Gold, a former Israeli ambassador to the United Nations.

The Jewish state has come to consider Iran's nuclear bid as an existential threat after incumbent hardliner President Mahmoud Ahmadinejad repeatedly called for the destruction of Israel during his four years in office.

Prime Minister Benjamin Netanyahu has said the threat posed by the Islamic republic was the biggest Israel has faced since its founding in 1948.

Israel also accuses Iran of funding, training and supplying weapons to radical groups such as the Lebanese Hezbollah militia and the Palestinian Hamas movement, which have both fought wars against Israel.

Israel, widely considered to be the Middle East's sole if undeclared nuclear armed state, suspects Iran is using its nuclear programme to develop atomic weapons, a charge Tehran has long denied.

The Jewish state has refused to rule out launching military strikes against Iran's nuclear sites and the Islamic republic has, in turn, vowed retaliation.

"Israel reserves its right to defend itself," Netanyahu said after talks with Obama in May.

Ultra-nationalist Foreign Minister Avigdor Lieberman said in June however that Israel was "not intending to bomb Iran."

Despite the intensifying rhetoric in recent years, the next Iranian president will have a chance to mend three decades of broken relations with Washington and pursue a negotiated solution to the nuclear standoff.

But Israel has expressed scepticism over the dialogue between its arch enemy and its closest ally, with talks also suspended between Iran and Western powers on the nuclear front.

US Defence Secretary Robert Gates said this week that Washington was increasingly concerned about advances in Iran's nuclear and ballistic missile programmes.

"Our concern with Iran, with Iran's programmes -- and I believe I can say also Israel's -- has continued to grow given the unwillingness of the Iranians to slow, stop or even indicate a willingness to talk about their programmes."

Ahmadinejad's leading challenger, moderate former premier Mir Hossein Mousavi, has promised to work to improve Iran's relations with the outside world but Israeli analysts doubt he would change the nuclear policy.

"The standoff with Iran will reach its peak at the end of the year and then we will see if the pragmatic leadership, if elected, will accept international and US pressure or choose confrontation," said Ely Karmon from the Inter-Disciplinary Centre in Herzliya.

The coming months will be pivotal as Israel's intelligence services believe Iran is getting close to acquiring nuclear weapons, possibly by next year.

Menashe Amir, an expert in Iranian affairs, said a moderate president who brought a shift in tone from Ahmadinejad's fiery rhetoric may, in fact, hamper international efforts to halt Iran's nuclear programme.

"If the real policy remains the same but the tone becomes softer, Iran would be able to dupe the West while it continues to develop its nuclear programme and plot in Afghanistan, Pakistan and prevent peace between Israel and the Palestinians," Amir told AFP.