Flags fly half-mast across the republics.
At 1pm today a mourning procession will march from Republic Square to the Yerablur military pantheon.
Prime Minister Nikol Pashinyan and other government officials are expected to participate.
A requiem service for the peace of souls of the heroes killed in Artsakh war will be offered at the Mother See of Holy Etchmiadzin on December 20.
The service will follow a Holy Liturgy chaired by His Holiness Karekin II, Supreme Patriarch and Catholicos of All Armenians.