Russian president Vladimir Putin made a proposal concerning Iran's nuclear programme to Tehran's leader at a private meeting during his brief stay in the country.
Iran's top nuclear negotiator Ali Larijani said Mr Putin had given a "special message" to Ayatollah Ali Khamenei, although what was said has not been disclosed.
Mr Larijani added that Mr Khamenei in turn told the Russian leader that Iran is co-operating with the UN nuclear watchdog, but is serious about continuing with uranium enrichment.
Mr Khamenei, who has the final say on all government matters in Iran, added that Iran will give Mr Putin's proposal serious thought before giving a response.
"We will ponder your words and proposal," the IRNA news agency quoted Mr Khamenei as saying.
Insiders close to Iranian officials said they believe the proposal from Mr Putin was a type of "time-out" on sanctions against Iran if Tehran suspends uranium enrichment.
The five permanent UN Security Council members, plus Germany, have been working together to try to find a way to get Iran to abandon its disputed uranium enrichment programme.
"The main reason for Putin's visit to Iran was to convey this message personally to the ultimate power in Iran," one official close to Tehran's leaders said.
Mr Putin's visit, during which he also met Iranian president Mahmoud Ahmadinejad and attended yesterday's summit of Caspian Sea nations, was a first.
No Kremlin leader has travelled to Iran since Josef Stalin in 1943 for a wartime summit with Winston Churchill and Franklin Roosevelt.
Before visiting Iran, Mr Putin held extensive talks on Iran's nuclear activities with some Western leaders, including French President Nicolas Sarkozy and German Chancellor Angela Merkel.
Mr Putin has bluntly spelled out his disagreements with Washington, saying last week that he saw no "objective data" to prove Western claims that Iran is seeking nuclear weapons.
At talks last Friday with US Secretary of State Condoleezza Rice and US Defence Secretary Robert Gates, he ridiculed America's plans for a missile defence system in eastern Europe, supposedly to stop an Iranian attack.
Yesterday in Tehran, Mr Putin warned the US not to use a former Soviet republic to stage an attack on Iran.
Iran insists the nuclear programme is only for developing energy, and it has touted the programme as a sign of its technological prowess. But the US and its allies contend Iran is secretly pursuing nuclear weapons.
In June 2006, the Security Council permanent members offered a package of economic and political rewards to Iran and a suspension of the implementation of sanctions if it agreed to suspend enrichment before the start of negotiations. Iran rejected that proposal.
The UN Security Council imposed sanctions on Iran in December for refusing to suspend enrichment, and modestly increased them in March after Tehran stepped up the programme. Iran responded by giving the UN nuclear watchdog less access to its nuclear facilities.