The military forces of Azerbaijan and Nagorno-Karabakh have reported another deadly clash in an ongoing flare-up of fighting.

Nagorno-Karabakh is a separatist region of Azerbaijan, which has been under the control of Armenia's military and a local force of ethnic Armenians since an all-out war ended in 1994.

Each side frequently accuses the other of violating the truce, but the recent escalation appears to be unusually intense.

Azerbaijan's Defense Ministry said Monday that three of its troops were killed and a "significant number" were wounded over the past day.

Nagorno-Karabakh military forces denied any losses, but acknowledged causing casualties among Azerbaijani troops.

On Saturday, Armenia accused Azerbaijan of firing 122-millimeter howitzers for the first time since the truce, and Nagorno-Karabakh said four of its fighters were killed in the barrage.