By Lucy Papachristou

LONDON (Reuters) -Armenian authorities on Wednesday arrested a prominent Christian cleric, Archbishop Bagrat Galstanyan, and accused him of orchestrating a plot to overthrow the government.

In a statement, Armenia's Investigative Committee said Galstanyan and alleged co-conspirators had "acquired the means and tools necessary to commit a terrorist attack and seize power".

Prime Minister Nikol Pashinyan wrote on his Telegram channel that the authorities had thwarted a "large and sinister plan by the 'criminal-oligarchic clergy'" to take power in Armenia.

It was the second arrest this month of a prominent government opponent, after Russian-Armenian real estate billionaire Samvel Karapetyan was detained on accusations of making public calls to usurp power.

Reuters was not able to immediately contact a lawyer for Galstanyan. Lawyers for Karapetyan say the businessman denies wrongdoing.

Pashinyan rose to power on a wave of street protests in 2018, but came under heavy domestic pressure after major losses to Azerbaijan in a brief war in 2020. In 2023, Azerbaijan retook the whole of the mountain enclave of Nagorno-Karabakh, where ethnic Armenians had enjoyed de facto independence for decades.

Tapping into popular anger over defeats and territorial concessions, Galstanyan and his supporters led days of street protests last summer to demand the removal of Pashinyan.

Detailing the charges that he faces now, authorities alleged that Galstanyan and associates had recruited over 1,000 people, mainly former soldiers and police officers, to block roads, paralyse traffic, incite violence and shut off the internet, with the goal of destabilising the government and seizing power.

The Investigative Committee published audio recordings purporting to show Galstanyan and others discussing plans for the alleged coup attempt.

Pashinyan, who faces parliamentary elections in June 2026, has moved towards signing a peace treaty with Azerbaijan, although tensions between the two countries remain high and the number of reported ceasefire violations has surged this year.

Armenia, formerly part of the Soviet Union, shares borders with Georgia, Azerbaijan, Turkey and Iran. It is a treaty ally of Russia, but relations with Moscow have been strained in recent years.

Asked about the alleged coup plot, Kremlin spokesman Dmitry Peskov said it was an internal matter for Armenia but Russia had an interest in calm and order being preserved there.

(Reporting by Lucy Papachristou; Editing by Mark Trevelyan)