A small home-made bomb went off Tuesday outside a central Moscow police station, injuring a policeman who found a suspicious package on the street, the RIA Novosti news agency reported.
The bomb was hidden inside a plastic bag left outside a department of internal affairs building, the news agency quoted an unnamed police source as saying.
The official did not specify the extent of the policeman's injuries, saying only that the bomb had the force equivalent of 50 grams of TNT.
Moscow was hit by three small blasts that all went off near Russian security service buildings in March, causing no casualties but prompting investigators to probe a suspected terror link.
A suicide bomb blast at Moscow's main airport killed 37 people in January in an attack claimed by Islamist rebels from the mostly Muslim North Caucasus region.