Bulgaria has expressed deep concern about “massive violations of the ceasefire” in the disputed region of Nagorno-Karabakh and called on Armenia and Azerbaijan to renew their efforts to find a peaceful solution to the conflict.

“We call on the parties to refrain from the use of force and escalation of tensions, and expect them to observe strictly the ceasefire,” the Bulgarian Foreign Ministry said in a statement on Monday.

Bulgaria reiterated its position that the conflict could only be solved through peace talks mediated by the OSCE Minsk Group of negotiators in the Nagorno-Karabakh conflict, the assistance of the European Union, as well as through active dialogue between the leaders of Armenia and Azerbaijan, according to the statement.

France, a co-president of the Minsk Group, said on Monday the group would meet on Tuesday in Vienna to discuss the outbreak of violence between Azerbaijan and Armenian-backed separatists in the South Caucasus mountain enclave.

Clashes on Saturday claimed the lives of at least twelve Azerbaijani servicemen, 18 Armenian troops and two civilians. On Sunday, Azerbaijan announced a unilateral ceasefire.

Both sides have accused each other of continuing to fire on Sunday across the frontline that has divided them since a war that saw Armenian separatists taking control of the region from Azerbaijan ended with an inconclusive truce in 1994.

Armenia and Azerbaijan, when joining the Council of Europe in 2001, both committed themselves to use only peaceful means for settling their conflict over the disputed region inside Azerbaijan inhabited predominantly by ethnic Armenians.

Nagorno-Karabakh, which was an autonomous region during Soviet times, has been at the centre of a dispute between neighbouring Armenia and Azerbaijan since they became independent states in the early 1990s.