Militants from the volatile North Caucasus had planned to stage a "major" terror act just outside Moscow, the head of Russia's state security agency services told President Dmitry Medvedev on Monday.
"One of major terror acts was averted in the Moscow region several days ago," FSB chief Alexander Bortnikov told the Kremlin chief.
He said in televised remarks the agency had detained four people from the restive Northern Caucasus, adding the militants had planned to target public places and "transport infrastructure" in the Moscow region.
The FSB also confiscated several explosive devices carrying 10 kilogrammes (22 pounds) of TNT equivalent, arms and maps, Bortnikov told Medvedev.
Russia is battling a insurgency in the North Caucasus where attacks on officials are a daily occurrence and after a lull of several years, suicide attacks returned to Moscow.
A suicide bomber from the North Caucasus killed 37 people at Russia's busiest airport Domodedovo in January. Two female suicide bombers from that region killed 40 and wounded dozens on the underground during morning rush hour last year.