It is "unclear" whether Russian President Vladimir Putin's planned visit to Iran on Monday will go ahead, his spokesman has said. "I can't confirm or deny that this visit will happen," Dmitry Peskov told the BBC, without elaborating.
Earlier, the Interfax news agency cited unnamed Russian security service sources as saying suicide bombers were plotting to kill Mr Putin in Tehran. Iran's foreign ministry dismissed the reports as "completely baseless".
Foreign ministry spokesman Mohammad Ali Hosseini said Mr Putin was due to arrive in Tehran on Monday evening, before attending a summit of Caspian Sea heads of state on Tuesday. Mr Putin would be the first Russian leader to visit Iran since Soviet dictator Joseph Stalin went there in 1943.
Mr Putin is currently in Germany meeting Chancellor Angela Merkel, with Iran's nuclear plans on the agenda. The US accuses Iran of seeking to develop nuclear weapons - but Iran insists its programme is entirely peaceful.
'Erroneous reports'
Mr Peskov declined to comment on whether the uncertainty surrounding MrPutin's visit was linked with the reports of an assassination plot. But he said that all would become clear "very soon".
On Sunday, Interfax said that according to Russian security service sources, several groups of suicide bombers had been preparing for an attack in Tehran The services had relied on information received from several unnamed sources outside the country, the agency said.
Mr Peskov earlier told Reuters that "the information is being dealt with by the secret services", adding that the president had been informed. Meanwhile, Mr Hosseini said the reports were "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. Russia is helping to build the controversial Bushehr nuclear power plant in southern Iran.
'Radical organisations'
A member of the Russian parliament's security committee, Gennady Gudkov, said the reports were likely to have a "fairly high level of reliability". "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 the Black Sea resort of Yalta. In 2003, police in London said they had arrested two men in connection with another plot to assassinate him.
(BBC News)