Armenia did not attend a summit of a Russian-led military alliance of former Soviet states, despite Russian President Vladimir Putin's call for unity.

The summit of the Collective Security Treaty Organization, or CSTO, was held in the Belarusian capital of Minsk on Thursday.

Putin said the CSTO has been making efforts to improve collective rapid deployment forces. He stressed that the CSTO member states, including Russia, do not tolerate terrorism in any region of the world.

Belarusian President Alexander Lukashenko said the alliance plays an integral role in ensuring the security of its members and the entire Eurasian region.

But Armenian Prime Minister Nikol Pashinyan did not attend the summit, in an apparent show of dissatisfaction with Russia. Armenia has relied on Russia's backing in the past, but relations with Moscow have cooled after the defeat of ethnic Armenians by Azerbaijan in the military conflict over Nagorno-Karabakh.

Armenia has said it does not intend to withdraw from the CSTO, but Pashinyan also did not attend a summit meeting of former Soviet nations last month.

Russian presidential spokesperson Dmitry Peskov expressed regret at Pashinyan's absence from the CSTO summit.

Putin is seen as wanting to strengthen the unity of the CSTO nations to counter Western countries, amid increasing tension over the war in Ukraine.