Russian special services have received a warning of a plot to assassinate President Vladimir Putin when he visits Iran on Tuesday.
In an unsourced report, Interfax said security services had been told that suicide bombers and kidnappers were training to kill or capture Mr Putin.
Interfax quoted Kremlin sources as saying they had no comment on the report, but the president had been informed.
However, Iran's foreign ministry has dismissed the report as 'completely without foundation'.
Mr Putin, who will be the first Kremlin chief to visit Iran since Soviet leader Josef Stalin went in 1943, will formally be in Tehran for a summit of Caspian Sea states.
But a meeting planned with Iranian President Mahmoud Ahmadinejad could give Mr Putin a chance to seek a peaceful compromise over Tehran's nuclear programme and to demonstrate his independence from Washington on Middle East issues.
Interfax is Russia's largest news agency and is often used by the Kremlin and government insiders as a means of communicating their message.