But further negotiations on the details lay ahead, and it was not known on Sunday whether Iran would entirely give up enrichment at home, a top demand of the West.
Gholamreza Aghazadeh, head of Iran's nuclear agency, and Sergei Kiriyenko, his Russian counterpart announced this in Bushehr, the site of Iran's first reactor, built with Russian aid and due to be inaugurated this year.
The deal could deflect any move by the UN nuclear watchdog agency at a 6 March meeting to recommend the Security Council consider action on Iran.
Mohammad Saeedi, Iran's deputy nuclear chief, warned that the deal would be off if the International Atomic Energy Agency refers Iran to the Security Council, a step that could lead to sanctions.
"If talk of referral is raised, then all ways will be blocked," Saeedi said.
No enriched material
Russian participation in the project is aimed at ensuring that no enriched material is secretly diverted to a weapons programme.
The US accuses Iran of seeking to develop nuclear weapons but has backed the proposal if it means enrichment would take place entirely in Russia.
Aghazadeh said the Bushehr
nuclear plant is 90% complete
Iran denies any intention to build weapons, saying it aims only to produce nuclear energy.
Stephen Hadley, US national security adviser, was cautious over the deal.
"It's too soon to say," he said on CNN's Late Edition. "In any of these arrangements, the devil is in the details. We'll just have to see what emerges."
It appeared that the issue of Iran's domestic enrichment was still unresolved between Tehran and Moscow. The nuclear chiefs of the two countries, while announcing the agreement, avoided addressing the issue.
Russia, a top ally of Iran, has been pressing Tehran to have all its uranium enrichment take place on Russian soil - and had made the deal contingent on Iran formally calling off its domestic enrichment programme, based in the central city of Natanz.
But Iran rejected that linkage, insisting on its right to carry out enrichment.
In tough negotiations over past weeks, Iran has said the location of enrichment and the degree of each side's role in the joint venture had to be worked out.
IAEA meets on 6 March to decide
on action against Iran
"We reached a basic agreement on the creation of a joint venture. How this is going to be created needs a lot of discussion and talks will continue in Moscow in the next few days," Aghazadeh said.
Kiriyenko said the Russian-proposed joint venture, if successful, would help achieve a peaceful solution to the standoff over Iran's nuclear programme.
"Russia has made its proposal to Iran for a joint uranium enrichment venture on Russian territory. If this proposal is carried out, a good opportunity will be created.
Negotiations about the creation of this venture are continuing actively," he said.
Bushehr nuclear plant
Kiriyenko suggested Russia would prevent any move by the IAEA at its 6 March session to put Iran before the Security Council.
"There is a possibility that Iran's nuclear activities can be resolved within the IAEA," he said.
"In any of these arrangements, the devil is in the details. We'll just have to see what emerges"
US National Security Adviser
Meanwhile, Aghazadeh said the Bushehr nuclear power plant was "90% complete" and that Iran will build two more 1000 megawatt nuclear power plants at the site.
Iran will issue tenders for the construction within a month, he said, suggesting Russia would be a favourite to build the plants.
"We will invite Russia and we will also be waiting for proposals (from others). Naturally, because of close and strategic relations between Iran and Russia, Iran will take this into consideration when granting the project," he said.
More than three years of IAEA probing have failed to produce concrete evidence of any Iranian nuclear weapons programme. But the agency discovered suspicious activity, including plutonium experiments and long-secret efforts to develop enriched uranium.
An IAEA team was in Tehran on Sunday, and Hamid Reza Asefi, the Iranian Foreign Ministry spokesman, said Iranian officials would discuss with the team a secret nuclear project that US intelligence has claimed was linked to warhead designed.
"We will discuss the issue, and the rumours surrounding it, with the agency. It is not very sensitive or ambiguous," Asefi said.