Russian President Vladimir Putin has been warned of a plot to assassinate him during a visit to Iran this week, Kremlin officials have said.
Vladimir Putin is due to visit Iran later this week
The Interfax news agency cited sources in the Russian special services saying a gang of suicide bombers would attempt to kill Mr Putin in Tehran.
Iran's foreign ministry dismissed the reports as "completely baseless".
A Kremlin spokesman told Reuters there were no plans to cancel the trip to meet President Mahmoud Ahmadinejad.
During his visit, Mr Putin will also attend a summit of Caspian Sea nations.
Mr Putin is currently in Germany meeting Chancellor Angela Merkel and is due to fly on to Tehran on Monday night.
Interfax reported that Russian special services said several groups of suicide bombers had been set up for the attack in Tehran.
The services had relied on information received from several sources outside the country, the agency said.
Kremlin deputy spokesman Dmitry Peskov told Reuters the trip was still going ahead as far as he was aware.
"The information is being dealt with by the secret services... The president has been informed," he said.
A spokesman for the Iranian foreign ministry, Mohammed Ali Hosseini, said the reports were completely baseless and "part of a psychological war waged by enemies to disrupt relations between Iran and Russia".
"Such erroneous reports will have no effect on the programme already decided upon for Mr Putin's visit to Tehran," he said.
Correspondents say Moscow and Tehran have good relations and Russia is helping to build the Bushehr nuclear power plant in southern Iran.
A member of the Russian parliament's security committee, Gennadiy Gudkov, said the reports were likely to have a "fairly high level of reliability".
"For me this report has not come as a big revelation, because, unfortunately, today there are enough radical organisations, forces and movements of an extremist nature, oriented against Russia, which would like to settle a score with the Russian president," he told the state-owned Russian news channel, Vesti TV.
"There are certainly organisations of this kind in Tehran, which in recent times has unfortunately been a stronghold of radical Islamic organisations," he said.
Russian officials have said several plots to assassinate Mr Putin on foreign trips have been uncovered since he became president in December 1999.
Shortly after his election, Ukrainian security services said they had foiled an attempt to kill Mr Putin at an informal summit of former Soviet republics in Yalta.
In 2003, police in London said they had arrested two men in connection with another plot to assassinate him.