It did not say how many victims were expected to be found at the sites, three of which could be so-called primary graves - or places where the dead were buried originally as opposed to pits to which they were later moved for concealment.
But Amor Masovic, of the Bosnian Muslim-Croat Federation Commission for Missing Persons, said that according to some sources the graves could hold up to 2500 bodies.
A statement from the Bosnian Serb government on Friday said "information (from) the Bosnian Serb authorities and witnesses led to new details about the Srebrenica events and helped locate 31 mass graves unknown to the wider public so far".
It said a commission investigating the 1995 Srebrenica atrocity, Europe's worst since the second world war, had visited the grave sites along with counterparts from the Muslim-Croat federation, postwar Bosnia's other autonomous half.
The commission was set up last year to investigate the Bosnian Serb seizure and sacking of Srebrenica and the killing of up to 8000 Muslim men and boys.
NATO forces have intensified the
hunt for war crimes suspects
Masovic said that eight of the mass grave sites he visited were completely new to his commission, which would start exhumation work in the next two weeks on one of the sites to clarify the validity of the findings.
Top peace envoy Paddy Ashdown sacked two senior Bosnian Serb officials, including the army chief-of-staff, when Bosnian Serb authorities failed to provide valid reports on the Srebrenica massacre.
The Bosnian Serb commission is under instructions from Ashdown to produce a full report by 11 June.
To date, dozens of mass graves containing thousands of Srebrenica victims have been unearthed on information provided by the UN war crimes tribunal and/or local witnesses.
Bosnian Serb wartime leader Radovan Karadzic and his military commander Ratko Mladic have both been twice indicted for genocide, their part in Srebrenica, and for the siege of Sarajevo during Bosnia's 1992-95 war.