Reading out a statement following a government meeting on yesterday's ruling, Justice Minister Nikola Selakovic suggested the work of the Hague-based court over the years was biased against Serbs and had left a "bitter taste".
"All justice that leads to the conviction of one people for crimes that were committed by everyone is selective," said Selakovic.
He added, however, that Serbia "must cooperate with" the tribunal and stressed he could not comment on specific verdicts.
He is the highest-profile figure to be convicted over the wars that tore Yugoslavia apart, with several others dying before they could face justice, and many Serbs believe the court has unfairly targeted them.
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The statement followed one from Serbia's traditional ally Russia, whose deputy foreign minister Gennady Gatilov also accused UN war crimes judges of bias and said Karadzic's verdict was "politicised".
The rally and verdict came on a politically-sensitive day for Belgrade -- the 17th anniversary of NATO launching a bombing campaign against Serbia in the Kosovo war.
At a memorial for victims of the bombing and again after the verdict, Prime Minister Aleksandar Vucic warned against attacks on Bosnia's Serb entity, the Republika Srpska, which was founded by Karadzic.
But Vucic, a former ultranationalist who now takes a staunchly pro-European stance, uncharacteristically did not address the press himself after today's meeting.
The 70-year-old will receive credit for time already spent in detention since 2008, and women in Srebrenica widowed by the slaughter slammed yesterday's sentence as "inadequate".