A blast at a bus shelter near Moscow's FSB secret police academy has damaged several parked cars but caused no injury, police say.
An unidentified device exploded in snow at the stop on Michurinsky Avenue around 1630 (1330 GMT), the FSB's national anti-terrorist committee said.
Two or three cars and the bus stop itself were damaged, it added.
No theory for the explosion was given. Moscow has seen several bomb attacks on its transport system in recent years.
Police sources told Russia's Interfax news agency that the explosion had occurred opposite No 70 Michurinsky Avenue - the FSB academy is located at No 90.
A spokesman for the FSB told AFP news agency it was too early to say if the explosion had been directed at the academy.
The FSB leads Russia's fight against militant groups based in the North Caucasus which have attacked Moscow and other Russian cities in recent years.
A suicide bomber attacked the arrivals hall in the city's Domodedovo international airport on 24 January, killing 37 people and injuring about 180.
The most recent attack on the city's Metro came in March 2010, when 39 people were killed by two suicide bombers.