Serbia has accused Croatia of obstructing its negotiations on European Union membership and said it would not submit to blackmail by its neighbor.
Serbian Prime Minister Aleksandar Vucic said his government was "stunned by Croatia's decision not to support Serbia's European path."
His statement on April 8 comes after Croatian officials in Brussels refused to give their assent to Serbia opening talks on a new chapter or policy area in the negotiations.
"Serbia will not allow itself to be blackmailed, humiliated, or disrespected by anyone," Vucic said in a statement. "Serbia will never be anyone's punching bag."
A row has been brewing since Croatia said this week that Serbia must change its law on prosecuting crimes committed during the 1990s Balkan wars as a condition for completing its EU membership negotiations.
Croatia says it is unacceptable for Serbia to claim jurisdiction for war crimes committed on the entire territory of the former Yugoslavia.
Croatia fought a 1991-95 war against Belgrade-backed Serbian rebels to forge its independence from Yugoslavia.