(Reuters) - Thirteen buses carrying around 300 refugees from the besieged Ukrainian city of Mariupol have arrived in Russia's Rostov region, Russia's Interfax news agency cited the Russian defence ministry as saying on Thursday.

       Ukrainian officials said on Wednesday civilians waiting in line for bread and sheltering in a theatre in Mariupol had been killed by Russian forces. Russia has denied attacking the theatre.

       (Reporting by Reuters; Editing by Jacqueline Wong)