A Russian air strike on a theatre in the Ukrainian city of Mariupol where hundreds of civilians had been sheltering in March was a "clear war crime" that killed at least a dozen people, human rights group Amnesty International said. In a report, Amnesty said Russian forces "most likely intentionally targeted" the building knowing it was a civilian site, "most likely" using two 500kg bombs that struck close to one another and detonated simultaneously. Amnesty also said its investigation found no convincing evidence to support other possible explanations, including a claim by the Russian defence ministry that the attack had...