Two bombs were detonated in the entrance hall of a residential building for employees of Russia's Federal Security Service in north Moscow on Friday, injuring no one, a police spokesman said.
The blasts occurred on Milashenkov Street close to Timiryazevskaya metro station at around 4:30 pm Moscow Time (13:30 GMT).
Each bomb was equivalent to 200 grams of TNT, a police source said.
On Wednesday an explosion ripped through a bus stop outside a training school for the FSB in southern Moscow, injuring no one.
A police source told RIA Novosti that one criminal group was probably responsible for the two blasts.
"Data gathered from probes into Wednesday's explosion on Michurinsky Prospekt and Friday's blasts on Milashenkov Street, suggests that the blasts were carried out by the same people," the police source said.
Both explosions have been classified as hooliganism.
MOSCOW, March 11 (RIA Novosti )