Russia's defence ministry said on Monday that 20 civilians had been killed and 28 wounded when a Ukrainian missile with a cluster charge exploded in the separatist-controlled city of Donetsk in eastern Ukraine.
The ministry provided no evidence and Ukraine denied launching an attack, which came as Russian forces were shelling the Ukrainian capital Kyiv and other cities more than two weeks after invading.
Reuters could not independently verify the statements by either side. Russia calls its actions in Ukraine a “special operation” to demilitarize and “denazify” its southern neighbour. Ukraine and its Western allies call this a baseless pretext for a war of choice.
“It is unmistakably a Russian rocket or another munition, there's not even any point talking about it,” Ukrainian military spokesman Leonid Matyukhin told a televised briefing.
Pro-Russian separatists who control part of Ukraine's Donetsk region said earlier that a child was among those hit in the alleged strike and they accused Kyiv of committing a war crime.
Ukraine has denied suggestions it would try to recapture the eastern cities of Donetsk and Luhansk, under the control of Russian-backed forces since 2014, by force.
Ukraine and its allies have previously accused Russia of planning “false flag” operations to create pretexts for further military offensives against Ukraine.
Asked about reports of a Ukrainian attack on Donetsk, Kremlin spokesman Dmitry Peskov said it was a tragedy.
Russian state news agency RIA Novosti carried photographs with a watermark reading “Donetsk People's Republic territorial defence headquarters” which appeared to show bodies lying on the ground, with separatist militia and a fire truck on the scene.
Video shot by a Reuters photographer in the centre of Donetsk showed damaged and burned-out vehicles. Several bodies and a fragment of missile with smoke rising from it were visible.
Reuters wrote to the press secretary of the head of the self-proclaimed statelet surrounding Donetsk seeking comment but she did not respond.
The UN human rights office said last week that it had received “credible reports” of several cases of Russian forces using cluster munitions in populated areas in Ukraine, adding that indiscriminate use of such weapons might amount to war crimes.
Russia has not responded to that assertion. It denies targeting civilians and has called a Ukrainian accusation it bombed a maternity and children's hospital in Mariupol “fake news”.