NATO will not allow a security vacuum to develop in Bosnia and Herzegovina amid the current crisis, but political leaders must work together to resolve tensions, NATO Secretary-General Mark Rutte said on Monday.

Tensions have risen since a court last month sentenced Milorad Dodik, the pro-Russian president of Bosnia’s Serb Republic, to a year in jail and banned him from politics for six years for defying rulings by an international peace envoy.

Dodik rejected the verdict, and the Serb regional parliament barred the national police and judiciary from its territory. The constitutional court responded by temporarily suspending separatist laws it said were threatening Bosnia’s constitutional order and sovereignty.

Rutte said disrespect for Bosnia’s peace deal, constitutional order, and national institutions was “not acceptable.”

He was referring to the 1995 Dayton Peace Agreement, which ended the 1992-95 war that killed 100,000 people. The accord divided Bosnia into two autonomous regions—the Bosniak-Croat Federation and the Serb Republic (Republika Srpska)—linked by weak central institutions.

Under the agreement, NATO initially deployed a peacekeeping force in Bosnia, which was replaced in 2004 by the European Union’s EUFOR mission. NATO remains in a supporting role and can return if peace is threatened.

The crisis has deepened divisions between the West and Russia, which, along with Serbia and Hungary, has backed Dodik. Moscow has called the Bosnian court’s ruling “a strike on stability in the Balkan region.”

“This is not 1992, and we will not allow any security vacuum to emerge,” Rutte said after meeting Bosnia’s tripartite presidency. He urged its three members to “take responsibility.”

“This country is looking at the three of you. Make this country proud of this presidency and solve this problem,” he said.

Dodik, who has long advocated for the Serb Republic’s secession and unification with Serbia, has been accused by critics of fueling the ethnic and political tensions that led to Yugoslavia’s bloody breakup in the 1990s.