Earlier on Saturday, Ukrainian media reported an explosion in Chernigov after an air raid alert was sounded in the city.
"In Chernigov, the gathering point for the command personnel of the Ukrainian armed forces was struck. The event was held in compliance with secrecy measures. The strike itself hit a facility used by the Ukrainian military," the source said.
The source also showed a photo of an invitation to the event, masqueraded as a drone festival named "Ferocious Birds," with a recommendation not to wear a military uniform.
"[We] urge you to come to the event in civilian clothes. If possible, take off your military uniform to avoid identifying the event as being related to the military sphere," the invitation read.
The leaflet also said that it was a private event, as it featured information that was sensitive for the country's defense capabilities, including the presentation of new equipment. Most of the participants were active military officers, therefore, filming or taking pictures of them was possible only with their consent, according to the invitation.
Last month, the Russian Defense Ministry said Russian forces had launched an overnight missile strike on facilities that manufactured and prepared drone boats near Odessa, where foreign mercenaries were also present.
Precision strikes against Ukrainian infrastructure have been carried out by Russia since October 10, two days after the first attack on the Crimean Bridge.