Ukraine's military chief said Monday that a covert listening device was found in one of the offices where he works, and hinted without elaborating that bugs were detected in other locations.

Army Cmdr. Valeriy Zaluzhnyi commented to local media about Sunday's revelation by Ukraine's Security Service that during a routine sweep a bug was found in a room he used. The device was not working, the agency said.

Suspicion immediately fell on Russia amid the almost 22-month war between the two countries that is set to grind on into another year.

"I have several offices where I work. This happened in one of them," Zaluzhnyi said. "We checked (the room) and found (the device)," he said.

He added that listening devices were not only found in the office where he worked, but he didn't provide further details and left it unclear whether more than one device was found in the Ukraine General Staff premises.

The murky developments left lots of questions unanswered. Officials did not comment further.

The intelligence services of both Russia and Ukraine have been active during the war.

Ukraine's military intelligence chief has survived 10 assassination attempts carried out by the Russian state security service, or FSB, according to Ukrainian authorities. Last month, his wife underwent hospital treatment after being diagnosed with heavy metals poisoning.

Ukraine's spy agency, meanwhile, reportedly has been active in sabotage operations far behind the front line.

Artillery bombardments continue to claim civilians lives as the front-line fighting becomes bogged down by wintry mud and snow.

Two Ukrainian civilians were killed and at least two were injured over the previous 24 hours, the president's office reported Monday.

In the north, the Russian army shelled the village of Krasnopillia in the Sumy region, killing a civilian in his home and damaging residential buildings, it said. In the south, an 81-year-old man died on the street during an attack on the center of Kherson city.