Loud explosions heard in rebel stronghold Donetsk in east Ukraine - witness

DONETSK Ukraine (Reuters) - Loud explosions were heard in the centre of the eastern Ukrainian city of Donetsk on Monday, a Reuters witness said. Donetsk is at the heart of a rebel uprising against rule by Kiev and Ukrainian President Petro Poroshenko has vowed to retake the city as part of what Kiev calls its "anti-terrorist operation" against the separatists. (Reporting by Anton Zverev, writing by Elizabeth Piper, Editing by Timothy Heritage)