Ukrainian President Petro Poroshenko has described an attack on the government-held city of Kramatorsk in which at least seven civilians died as a "crime against humanity".

Mr Poroshenko made the comment on a visit to the city, on the eve of key peace talks in the Belarusian capital Minsk.

He told reporters that he demanded an "immediate, unconditional ceasefire" and the "withdrawal of foreign troops from Ukrainian territory".