Russian President Vladimir Putin on Sunday vowed to bring more "destruction" to Ukraine in retaliation for a drone attack on the central Russian city of Kazan a day earlier.
Russia accused Ukraine of a "massive" drone attack that hit a luxury apartment block in the city, some 1,000 kilometres (620 miles) from the frontier. Videos on Russian social media networks showed drones hitting a high-rise glass building and setting off fireballs, though there were no reported casualties as a result of the strike.
"Whoever, and however much they try to destroy, they will face many times more destruction themselves and will regret what they are trying to do in our country," Putin said during a televised government meeting on Sunday. Putin was addressing the local leader of Tatarstan, the region where Kazan is located, in a road-opening ceremony via video link.
The strike on Kazan was the latest in a series of escalating aerial attacks in the nearly three-year conflict.
Ukraine has not commented on the strike.
Putin has previously threatened to target the centre of Kyiv with a hypersonic ballistic missile in response to Ukrainian attacks on Russian territory. And the defence ministry has called Russian strikes on Ukrainian energy facilities over recent weeks retaliatory hits for Kyiv using Western-supplied missiles to hit Russian air bases and arms factories.
Kyiv on Sunday also accused Russian forces of killing captured Ukrainian soldiers -- an alleged war crimes violation. A video posted by Ukraine's 110th separate mechanised brigade showed "the shooting of soldiers who surrendered," Kyiv's human rights ombudsman Dmytro Lubinets said in a post on Telegram. He said the video -- aerial footage from a drone of an apparent confrontation between Russian and Ukrainian soldiers -- showed Russians shooting the Ukrainians at point-blank range after they had already surrendered. AFP could not verify the footage.