Vladimir Putin has lost a key ally in Europe as Armenia rages at Moscow over its stance on the country's conflict with neighbour Azerbaijan.

Armenia has effectively suspended its membership of the Collective Security Treaty Organization (CSTO), a group of former Soviet states.

But Armenian Prime Minister Nikol Pashinyan said on Tuesday that the group "hasn’t fulfilled its security obligations towards Armenia."

Speaking to France 24, he added: "This couldn’t have gone without consequences. And the consequence is that in practice we have basically frozen our participation in the CSTO."

Pashinyan accused Russia of failing to step in amid the conflict between Armenia and Azerbaijan, the latter not a member of CSTO.

In September, Azerbaijan launched a military operation to take the region of Nagorno-Karabakh, at the centre of conflict between the two countries for years.

As a result, 100,000 Armenians were forced to leave the area.

Russian troops had been in the region as peacekeepers but left prior to Azerbaijan's attack.

Many Russian soldiers remain stationed in Armenia but this could be threatened by Pashinyan's growing anger at Moscow.

Kremlin press secretary Dmitry Peskov said on Friday that Armenia has not officially notified Moscow of its intention to suspend its membership of the CSTO.

Nagorno-Karabakh lies in the mountainous South Caucasus region between the Black Sea and the Caspian Sea.

Azerbaijan and Armenia fought over the region in the 1980s and 1990s.

Tensions ramped up once again in 2020 when Azerbaijani forces recaptured all the territories surrounding Nagorno-Karabakh after an attack.

Russia brokered a peace deal after six weeks of fighting.