The European Union strongly supports Ukraine's sovereignty and territorial integrity, the bloc's Foreign Policy Chief Josep Borrell said Wednesday.

"I want to stress for the European Union, the territorial integrity and sovereignty of Ukraine is above anything," Borrell told reporters on the way to a NATO foreign ministers meeting in Riga, Latvia's capital.

"We will be standing firmly and decisively with a grain in front of any attempt to undermine its territorial integrity and sovereignty," he added.

He also warned that the EU and NATO must prepare for all kinds of scenarios, including Russia's potential use of aggression against the country, "to make sure we have a strong response."

He explained that he would discuss the concerning situation in the western Balkans with top NATO diplomats.

"We remain committed to Bosnia-Herzegovina as a single country. We call everyone to do the reforms necessary to keep this unity and to reform the electoral law," Borrell pointed out, referring to the country's political crisis stemming from the separatist intentions of Bosnian Serb leader Milorad Dodik.

He also called on Kosovo and Serbia to resume talks since there was "no other way to stabilize the situation."

The tension between the neighboring countries has risen over a dispute of border crossings and license plates since late September.

Top NATO diplomats gathered on Monday to discuss the most pressing security issues for the alliance, including Russia's military buildup in and around Ukraine, the Belarus border crisis and the situation in the western Balkans.

After the first day of their meeting, NATO Secretary-General Jens Stoltenberg warned that "aggression against Ukraine would come at a high price and have serious political and economic consequences for Russia."