* Khamenei says voters should disappoint Iran's enemies

* Iranians elect members of parliament and leadership body

* Reformists urge high turnout despite barring of candidates

* Many levers of power likely to remain in conservative hands

Iranians voted in two crucial elections on Friday, with Supreme Leader Ayatollah Ali Khamenei urging a big turnout in order to frustrate Tehran's foes, a remark reflecting the Islamic Republic's traditionally anti-Western policies.

The vote, Iran's first since last year's nuclear deal with world powers, could determine whether the Islamic Republic continues to emerge from diplomatic and economic isolation after years of sanctions.

"Whoever likes Iran and its dignity, greatness and glory should vote. Iran has enemies. They are eyeing us greedily. Turnout in the elections should be so high to disappointed our enemies ... People should be observant and vote with open eyes and should vote wisely," Khamenei said after casting his vote.

The contest is for parliament and the Assembly of Experts, a body that has the power to appoint and dismiss the supreme leader, Iran's most powerful figure. Both are currently in the hands of hardliners.

Supporters of pragmatist President Hassan Rouhani, who championed the nuclear deal and is likely to seek a second presidential term next year, are pitted against conservatives deeply opposed to detente with Western powers.

Influential former president Ayatollah Akbar Hashemi Rafsanjani, a veteran pragmatist politician allied to Rouhani, told Reuters that Iran would lose if reformists were defeated in Friday's contests.

Asked what would happen if reformists did not win, he said: "It will be a major loss for the Iranian nation."

Results hard to predict

Foreign Minister Mohammad Javad Zarif, who led nuclear talks with world powers, said while voting at a polling station at the Jamaran mosque in northern Tehran that Iranians would continue to support policies that brought about the nuclear deal.

"The message to the international community from this election is the Iranians are solidly behind their government," he said. "They will continue to support the policies that have been adopted leading to the conclusion and successful implementation of the nuclear deal and this will continue."

"Whatever the choice of the Iranian people, it will be respected," he said.

Both sides have called for a strong turnout. Most reformist candidates have been barred by a hardline clerical vetting body, along with many moderates, but their supporters have called on voters to back Rouhani's allies and keep the conservatives out.

Results are hard to predict, with conservatives traditionally doing well in rural areas and young urbanites favouring more reformist candidates.

At stake is control of the 290-seat parliament and the 88-member Assembly of Experts. During its eight-year term it could name the successor to Ayatollah Ali Khamenei, who is 76 and has been in power since 1989.

If the Assembly of Experts is called upon to choose a successor to Khamenei, its decision could set the Islamic Republic's course for years or even decades to come.

Mistrust of the West runs deep, and hardliners have sought to undermine Rouhani's allies by accusing them of links to Western powers.

Setting course

A more supportive parliament would allow Rouhani to continue his economic reforms at home and diplomatic engagement abroad.

Whatever the outcome, though, Iran's political system places significant power in the conservative establishment including the Guardian Council, the judiciary and the Supreme Leader.

The 12-member Guardian Council must approve all new laws and vet all electoral candidates. It has already played a role in Friday's vote by excluding thousands of candidates, including many moderates and almost all reformists.

Nevertheless, prominent reformists and moderates have scrabbled together a joint list of candidates in Tehran - 30 for parliament, and 16 for the Assembly of Experts - and hope this can propel them to an overall majority in both bodies.