Belarusian anti-government activists have claimed responsibility for what they said was a drone attack on a Russian A-50 surveillance aircraft at an airfield near the Belarus capital of Minsk on Sunday.

“Those were drones. The participants of the operation are Belarusian,” Aliaksandr Azarov, leader of Belarusian anti-government organization BYPOL, was quoted as saying on the organisation’s Telegram messaging app and on the Poland-based Belsat news channel.

“They are now safe, outside the country.”

Reuters was not able to independently verify the report of the attack. There was no official confirmation from Russia or Belarus and there was no immediate response from their defence ministries to requests for comment.

Belsat is a Polish broadcaster focused on Belarusian news that Minsk has branded extremists. BYPOL, which includes former law enforcement officers who support opposition politicians, has been branded a terrorist organization.

Franak Viacorka, an adviser to Belarusian opposition leader Sviatlana Tsikhanouskaya said in a post on Twitter it was the most successful act of sabotage since the beginning of 2022.

Front and central parts of the aircraft as well as the radar antenna were damaged as a result of two explosions in the attack at the Machulishchy air base near Minsk, BYPOL reported.

The Beriev A-50 aircraft, which has the NATO reporting name of Mainstay, is a Russian airborne early warning aircraft, with airborne command and control capabilities, and the ability to track up to 60 targets at a time.

Since the beginning of Russia’s invasion of Ukraine a year ago, there have been several acts of sabotage in Belarus and in Russian regions bordering Ukraine, especially on the railway system.

President Alexander Lukashenko of Belarus has not taken a direct part in Russia’s war on Ukraine, but he allowed its forces access to use the territory as a staging post at the beginning of the invasion a year ago.

Russia and Belarus have set up a joint military unit in Belarus and have held numerous exercises. A number of Russian warplanes and airborne early warning and control aircraft have been deployed to Belarus.

“I am proud of all Belarusians who continue to resist the Russian hybrid occupation of Belarus & fight for the freedom of Ukraine,” Tsikhanouskaya wrote on Twitter.

The Belarusian human rights group Vyasna said on Monday that a woman was detained in Machulishchy but the reason and her whereabouts were not known.

There was no information on whether the detention was related to the alleged sabotage of the aircraft.

Detentions are common in Belarus, for offences as small as comments on social media, especially after Lukashenko crushed the mass-pro-democracy protests in 2020 and jailed all leading opposition figures or forced them to flee abroad.