The former head of the armed forces in Serbia was convicted on Tuesday of crimes against humanity and war crimes by an international tribunal at The Hague.

The former official, Momcilo Perisic, was the army chief of staff of Yugoslavia in the 1990s when that crumbling nation was reduced to just Serbia and Montenegro, and he was a principal architect of the ethnic war in the breakaway republic of Bosnia and Herzegovina. He was charged in connection with attacks on civilians by soldiers under his command in Bosnia and Croatia, including in the cities of Sarajevo and Srebrenica, and he was sentenced on Tuesday to 27 years in prison.

The conviction of Mr. Perisic, 67, was the first by the tribunal against a Serbian official for crimes committed in Bosnia and Herzegovina, the court said.