SOFIA, Feb 8 (Reuters) - Bulgarian investigators charged former energy minister Alexander Nikolov on Wednesday with mismanagement that led to losses of more than 88 million levs ($48.36 million) at state gas firm Bulgargaz, related to Russia cutting off gas supplies to the country.

Russia cut the gas supplies on which Bulgaria was almost fully reliant at the end of April 2022 after the European Union country refused to pay for deliveries in roubles.

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Nikolov failed to properly supervise the former head of Bulgaria's public gas supplier Bulgargaz, Ludmil Yotsov, who is also charged with mismanagement, a spokesperson for Bulgaria's National Investigative Service told reporters.

"The former minister of energy is accused of failing to exercise sufficient controls over the former chief executive of Bulgargaz in connection with inaction to ensure the operational activities of Bulgargaz," the spokesperson told reporters.

"As a result, Bulgargaz incurred damages of 88 million levs from the end of April and May," the spokesperson said without elaborating.

Former deputy energy minister Danail Nikolov has been charged with malfeasance as part of the same probe.

The spokesperson said the probe was ongoing with investigators looking into how Bulgaria had formed its official position on the payment scheme proposed by Russia's Gazprom and other activities linked to gas supplies last spring.

Nikolov denied any wrongdoing and told reporters that during his time in office from December 2021 to August 2022 the public interest was fully respected.

"The essence of the charges lies in the fact that Bulgaria refused to bend to the Russian blackmail," he wrote on his Facebook page.

Reuters was unable to immediately contact Ludmil Yotsov and Danail Nikolov for comment.

The centre-right GERB party has accused the former government of reformist Kiril Petkov of paying higher prices to secure alternative gas supplies after it refused to pay for Russian gas in roubles.

Bulgargaz initially secured replacement natural gas imports mainly from neighbouring Greece.

Petkov's coalition government, where Nikolov was energy minister, was toppled in a no-confidence vote six months after taking office in December 2021.

In a statement on Wednesday, Petkov's anti-corruption We Continue the Change party, a key rival of GERB ahead of new snap polls in April, decried the charges and said Nikolov was accused for following European Commission's recommendations on how to proceed with the contract with Gazprom.

The party reiterated it had refused to bend to the Russian pressure and had secured two shipments of liquefied natural gas at prices equal to those under the contract with Gazprom.

($1 = 1.8196 leva)

(Reporting by Tsvetelia Tsolova; Editing by Kirsten Donovan and Josie Kao)