Border clashes around Nagorno-Karabakh have left five soldiers dead, Azerbaijan's Defense Ministry said Saturday.

Azerbaijan vowed to retaliate to Armenian attacks with heavier weapons after an Azerbaijani soldier was killed and three wounded in artillery strikes. The defense ministry said four Armenian soldiers were killed and 16 wounded in response.

Clashes between the two started in 1988 with the invasion of the Azerbaijani territory of Nagorno-Karabakh by Armenia, and later evolved into a full-fledged war in 1992.

Since the end of the war in 1994, Armenian and Azerbaijani delegations have held talks over the status of Nagorno-Karabakh under the supervision of the Organization for Security and Co-operation in Europe's Minsk Group.

Although a cease-fire was signed in 1994, clashes regularly occur along the border.