"Regarding this joint venture, we have reached a basic agreement," Iran's nuclear chief Gholamreza Aghazadeh said in the southern Iranian port of Bushehr on Sunday.
Russia has offered to enrich uranium for Iran to ease world concerns over Tehran's nuclear programme, but the latest round of talks in Moscow last week brought no visible progress.
The Russian proposal, backed by the US and the European Union, is intended to assuage concerns that enrichment conducted in Iran could produce material for atomic weapons.
Sergey Lavrov, the Russian foreign minister, said on Sunday that Moscow will continue its efforts to help resolve the Iranian nuclear crisis until a planned meeting of the UN's nuclear watchdog agency in just over a week.
The 6 March meeting of the International Atomic Energy Agency could start a process leading to punishment by the UN Security Council, which has the authority to impose sanctions on Iran.
Aghazadeh: A basic agreement
"Contacts will continue until the IAEA board meeting on 6 March," Lavrov said in televised remarks.
Iran says it is pursuing peaceful nuclear energy, but Western nations fear it is seeking an atomic weapon.
Sunday's announcement came as Russia's top nuclear official, Sergei Kiriyenko, visited the construction site of an atomic-power plant his country has been building for Iran in the Gulf coast city of Bushehr.
According to the Itar-Tass Russian News Agency, Kiriyenko was also to discuss delivery schedules of Russian fuel bound for the Bushehr plant.
On Saturday, Kiriyenko expressed confidence that the IAEA could still resolve a standoff over Iran's programme that may lead to Security Council sanctions against the Islamic republic.
Also on Sunday, Iran played down a secret nuclear project that US intelligence has linked to warhead design, saying it would offer information on it to the IAEA.
"We will discuss the issue, and the rumors surrounding it, with the agency. It is not very sensitive or ambiguous," Hamid Reza Asefi, Iranian's Foreign Ministry spokesman, said when asked about the secret project known as Green Salt.
Asefi confirmed that an IAEA team was in Tehran to discuss the country's nuclear programme.
Public mention of the Green Salt Project first surfaced in an IAEA report drawn up earlier this month for a meeting of the agency's 35-nation board of governors.