Armenia’s Prime Minister Nikol Pashinyan announced that his country would pull out of the Collective Security Treaty Organization (CSTO).
Mr Pashinyan accused members of the alliance of siding with Azerbaijan which launched a military campaign in September to seize control of the Nagorno-Karabakh region.
Armenia’s ties with Russia have become strained since Moscow refused to intervene in the Nagorno-Karabakh conflict. Russia had acted as guarantor of a peace deal that ended a 44-day war with Azerbaijan over the disputed territory three years ago.
The CSTO is a Russia-dominated alliance of former Soviet states that have pledged to protect one another in the event of an attack.