LVIV, Ukraine (Reuters) - Authorities in the Ukrainian city of Mariupol said on Thursday it was still not possible to estimate the number of possible casualties from what they said was an air strike on a theatre where hundreds of people were believed to have been sheltering.

       "Yesterday and today, despite continuous shelling, rubble is being cleared as much as is possible and people are being rescued. Information about victims is still being clarified," the city council said in an online statement about Wednesday's incident.

       It provided no figures on the number of people rescued. Russia has denied bombing the theatre.

       (Reporting by Pavel Polityuk, Writing by Alessandra Prentice, Editing by Timothy Heritage)