BUSHEHR, Iran: Iran has reached a "basic" agreement with Russia on jointly enriching uranium, officials said on Sunday - but there was no immediate sign that it would suspend home-grown enrichment to allay fears that it is developing nuclear weapons.

It was unclear what this basic agreement involved and both Russian and Iranian officials identified serious obstacles to a full deal.

These principally concerned a suspension of Tehran's home-grown uranium enrichment work, the main demand of Western powers who are threatening to press for UN sanctions.

The original Russian proposal had been for Iran's uranium to be enriched in Russia to defuse suspicions that Iran might divert some nuclear fuel into a weapons program.

However, Iran has always insisted upon its right to enrich the uranium it mines in its central desert on its own soil, and it was unclear how the original Russian proposal could be tailored to please Tehran.

"Regarding this joint venture, we have reached a basic agreement. Talks to complete this package will continue in coming days in Russia," Iranian nuclear chief Gholamreza Aghazadeh told reporters in the Iranian port town of Bushehr.

But Sergei Kiriyenko, head of Russia's atomic energy agency, speaking at a news conference with Aghazadeh, said Iran still had to take "serious steps" before the deal could be completed.

He did not specify what these would be, but an unnamed Russian official in Bushehr told Interfax news agency that the deal could only go ahead if Iran suspended its own uranium enrichment - something it has repeatedly refused to do.

Aghazadeh also stipulated that Iran would be setting an unspecified "precondition" to the deal.

One EU diplomat said this precondition was almost certain to be Tehran insisting upon its right to enrich its own uranium.

"Their idea of accepting the Russian proposal is to be able to enrich in Russia and Iran, not just Russia," he said on condition of anonymity.

Europe and Washington have said they could not accept such a compromise.

Iran has already been reported to the UN Security Council - which has the power to impose sanctions - after failing to convince the world that its nuclear ambitions are entirely peaceful. Tehran flatly denies trying to develop nuclear arms.

Konstantin Kosachev, head of the foreign relations committee in Russia's lower house of parliament, the State Duma, said the chances of an agreement were about 50-50.

"(Tehran) is now using the tactic of dragging out talks as long as possible. I do not think we can expect Iran to clarify its position any time soon. I would rather suggest that this will not happen before March 6," he told Interfax.

March 6 is the date when the board of the United Nations' watchdog, the International Atomic Energy Agency (IAEA), meets to discuss the IAEA's latest report on Iran's nuclear program.

The report may determine whether the United States and European powers pressure the Security Council to impose sanctions.

Diplomats said the talk of an agreement could be an attempt to soften the IAEA report. Kiriyenko said the issue could still be solved without Security Council referral.

"There are solutions to resolve Iran's issue within the framework of the IAEA," he said in Bushehr, where Iran is building its first nuclear power station with Russian help.

Aghazadeh said Iran would formally invite tenders in a month for contracts to build two further 1,000-megawatt power stations in Bushehr, and that Russian applications would be welcome.

Meanwhile, the launch of Iran's first nuclear power station, being built near the southern city of Bushehr with Russian help, has been delayed again, an Iranian official said Sunday.

The head of Iran's nuclear power station development program said "the start-up will be delayed a bit" - but did not give any new date for the scheduled firing up of the facility.