By Mark Trevelyan LONDON (Reuters) – Russia shifted its stance over the bombing of a Ukrainian hospital in the city of Mariupol, with a mix of statements on Thursday that veered between aggressive denials and a call by the Kremlin to establish clear facts. Ukrainian President Volodymyr Zelenskiy said three people including a child had been killed in the bombing on Wednesday, and rejected Russian assertions there had been no patients there. “Like always, they lie confidently,” said Zelenskiy, who has accused Moscow of waging genocide in the war it launched two weeks ago. In the face of worldwid…