KYIV (Reuters) -Ukrainian authorities said on Sunday they had opened an investigation into alleged shootings by Russian forces of six unarmed Ukrainian soldiers in the city of Avdiivka, and two at a village in the same region, after Russia claimed full control of the city. "An investigation into the shootings of unarmed Ukrainian prisoners of war in Avdiivka and Vesele has been launched," the prosecutor's office in Donetsk region said on its Telegram channel.