Iran on Monday urged "honesty" at crucial talks with world powers due to be held this week in order to defuse a tense international showdown over its disputed nuclear activities.

"We hope the P5+1 will come to the negotiating table with honesty, and we also will make an honest effort so that both sides reach a win-win conclusion," Foreign Minister Ali Akbar Salehi told the Iranian parliament's website.

Salehi warned the P5+1 group -- consisting of UN Security Council members the United States, France, Britain, Russia and China, plus Germany -- should not try to impose conditions on the talks before they begin on Saturday in Istanbul.

The aim was that "Iran gain its rights and the P5+1 have its stated concerns alleviated" over Tehran's nuclear programme, he said.

The United States and its allies fear Iran's nuclear activities mask a drive towards atomic weapons capability -- something Tehran strenuously denies. The United States and Israel have threatened to launch attacks on Iran if diplomacy on the issue fails.

Salehi rejected a weekend report in The New York Times newspaper quoting unnamed US and EU diplomats as saying the West was going into the talks with demands that Iran close an underground nuclear bunker in Fordo, and that it halt enriching uranium to 20 percent.

"Those (demands) have been raised only by the media and we cannot make a judgment based on them," Salehi said.

"Putting forward preconditions before the meeting happens is equivalent to reaching a conclusion before the negotiations start. It is completely meaningless. No one will accept preconditions before the talks," he added.

His remarks echoed a statement on Sunday by the head of Iran's Atomic Energy Organisation, Fereydoon Abbasi Davani, that the reported Western demands were "irrational" and would not be accepted.

Salehi did not speak about the venue of the talks or Iran's see-sawing in recent days over whether the negotiations should be held in Istanbul.

The foreign minister had repeatedly said Iran favoured Istanbul. But other Iranian officials and politicians last week said they were opting for Baghdad instead.

The about-face by Iran exposed tensions with Turkey over its support of the opposition in restive Syria, Iran's main ally in the Middle East.

Turkish Prime Minister Recep Tayyip Erdogan last Thursday issued a rare and sharp criticism of Iran after it backed away from Istanbul, saying: "They continue to lose prestige in the world because of a lack of honesty."

By Monday, Iran appeared to have changed direction once more and was on board again for Istanbul to host the talks with the P5+1.

Iranian President Mahmoud Ahmadinejad said in a statement on his official website on Sunday that "Iran is ready for negotiations" and had unspecified "practical suggestions for the upcoming meeting."

The office of EU foreign policy chief Catherine Ashton, who is representing the P5+1, confirmed on Monday that "we have agreed to launch talks in Istanbul on April 14."

Spokesman Michael Mann added: "We hope that this first round will produce a conducive environment for concrete progress."

Iran's last talks with the P5+1 were also held in Istanbul, in January 2011, and ended in failure.