MOSCOW, Nov 15 (Reuters) – Russia said on Wednesday that Armenian Prime Minister's Nikol Pashinyan's decision to stay away from a summit of the Russia-led Collective Security Treaty Organisation (CSTO) was the latest anti-Russian move by Armenia orchestrated by the West.

Relations between Russia and Armenia, which are formally allies, have soured in recent months, with Yerevan publicly questioning the value of its partnership with Russia and trying to deepen ties with the West.

The trigger was Azerbaijan retaking its breakaway region of Nagorno-Karabakh in September, prompting almost all of the territory's 120,000 ethnic Armenians to flee despite the presence of Russian peacekeepers.

Some Armenians blamed Russia for failing to stop what Baku called an anti-terrorist operation, an allegation that Moscow has rejected.

Russian Foreign ministry spokeswoman Maria Zakharova told reporters that Russia saw Pashinyan's refusal to attend the CSTO summit as the latest in a "chain" of events.

"The West is obviously behind it. The West, whose plans in Ukraine have failed, is now gripping Armenia, trying to tear it away from Russia," she said.

Earlier on Wednesday, Armenian state news agency Armenpress cited Pashinyan as telling the country's parliament that the CSTO had repeatedly failed to protect Armenia's interests.

He said that Armenia was looking to diversify its security arrangements, but that it had not yet decided whether or not it would leave the CSTO.