Officials in the South Caucasus region of Nagorno-Karabakh say four of their soldiers have been killed in fighting with Azerbaijan.

Nagorno-Karabakh is officially part of Azerbaijan, but since a separatist war ended in 1994 it has been under the control of forces that claim to be local ethnic Armenians. Azerbaijan claims the forces include regular Armenian military. Efforts to negotiate a settlement have failed, and frequent clashes have continued.

Three of the men were killed Friday and a fourth Saturday morning, according to Nagorno-Karabakh's Defense Ministry. Azerbaijan's Defense Ministry said one of its soldiers was killed Friday.

Both sides blamed each other for the violence. 

The fighting is some of the deadliest since April 2016, when about 75 soldiers were killed on both sides.