Iran's supreme leader Ayatollah Ali Khamenei warned on Tuesday that the country's next president should avoid making "concessions" to the west, saying this would not ease tensions over Tehran's nuclear drive.

Khamenei, the ultimate decision maker in Iran, has the final say on all key issues, including its controversial nuclear programme, a major source of concern in the West over suspicions the Islamic republic is using it to develop weapons.

"Some (candidates) have the wrong analysis that by giving concessions to enemies, their anger towards Iran will be reduced," Khamenei said in a live televised speech. "This is a mistake."

His remarks came as Iran readies for elections on June 14 to replace President Mahmoud Ahmadinejad, during whose tenure the country has struggled to cope with severe international economic sanctions, in particular on the vital oil income.

Eight presidential candidates, most of them conservatives close to Khamenei, have been approved by the Guardian Council, a hardline electoral oversight body, to run in the election.

Addressing them directly, Khamenei said regardless of who wins the poll, they should "promise not to attach importance to the interests of foreigners more than they do to those of the Iranians."

He branded Iran's ailing economy, battered by high inflation and unemployment, as the "main issue" before the candidates.

"Economic problems exist, inflation exists, but God willing the next (president) will resolve these issues.

"If we can shore up the economy, the enemy will be left defenceless in its confrontation with the Iranian nation," said Khamenei, while calling on the next president to build up Iran's "national might" against Western hostility.

Almost all the candidates attended the ceremony at the shrine of the Islamic revolution's late founder, Ayatollah Ruhollah Khomeini, who died in 1989.

Among them were top nuclear negotiator Saeed Jalili, who represents Iran in talks with the so-called P5+1 countries, the United States, Britain, China, France and Russia plus Germany aimed at curbing sensitive aspects of the Iranian nuclear programme. Those talks have failed to produce a breakthrough.

Jalili has vowed, if elected president, to pursue a path of resistance against Western demands.

Moderate candidate Hassan Rowhani, an ex-nuclear negotiator, who did not attend the ceremony according to Iranian media, and Ali Akbar Velayati, a former Iranian foreign minister of 16 years, have both vowed to resolve the nuclear issue using their diplomatic records.

The nuclear issue has been a uniting factor in Iran's short election campaign, which started last week, with all candidates seeing eye to eye when it comes to what the Islamic republic terms as its "right" to operate a peaceful atomic drive.

On Tuesday, Khamenei insisted he did not have any "preference" when it came to the candidates and called on Iranians to cast their ballots on June 14, saying a high turnout would foil foreign attempts to undermine the election.

"Every vote for any candidate is a vote for the Islamic republic; it is a vote to confidence in the establishment and the electoral process," he said.

Last month, US Secretary of State John Kerry said it was "highly unlikely" that any of the eight approved candidates would "represent the broad will of the Iranian people or represent a change," while French foreign ministry spokesman Philippe Lalliot urged Iran to allow the people to "freely choose" their leaders.

The election campaign has been marred by the barring of two would-be frontrunners: moderate two-term ex-president Akbar Hashemi Rafsanjani, and Ahmadinejad protege Esfandiar Rahim Mashaie.

The Guardians Council has also disqualified all women from running.

The June 14 poll is Iran's first presidential election since 2009, when claims of voter fraud sparked massive street protests against the re-election of Ahmadinejad.

Presidential candidates turned opposition leaders Mir Hossein Mousavi and Mehdi Karroubi, who called for demonstrations, have been held under house arrest incommunicado for more than two years.