Moscow — Even as Azerbaijan announced a unilateral cease-fire Sunday, reports of sporadic fighting between Azerbaijani and ethnic Armenian forces over the separatist enclave of Nagorno-Karabakh continued. Regional and world leaders called for an end to the worst violence in the region since a cease-fire halted a war over the territory in 1994.

Armenia and Azerbaijan, both former Soviet republics, fought a bloody ethnic war over the territory as the Soviet Union fell apart. About 20,000 people died. Formally a part of Azerbaijan, Nagorno-Karabakh is de facto controlled by a separatist government backed by Armenia and has increasingly been the site of sporadic border conflicts in recent years. Today, nearly all of its population is ethnically Armenian.

This weekend’s violence has been on a previously unseen scale, analysts said, with reports of the use of helicopters, drones, tanks and artillery along the “line of conflict” that separates the two sides.

Thirty soldiers and a boy were killed in fighting Saturday, as Azerbaijan claimed to have seized several strategic heights and several villages from the Nagorno-Karabakh government. Both sides blamed the other for the violence.

The United States and Russia have called for an immediate end to the fighting.

Turkish President Recep Tayyip Erdogan on Sunday said that he will stand with Azerbaijan “to the end” and that “we pray our Azerbaijani brothers will prevail in these clashes,” his office reported.