Two Ukrainian helicopters have been shot down and both their pilots killed in the eastern town of Slavyansk.
Pro-Russian separatists in the town said they were fighting back against a "large-scale operation" to retake the city by Ukrainian forces.
Reports emerged this morning that Ukrainian forces had launched what appeared to be their first major assault on rebels there.
Roland Oliphant, Moscow correspondent with The Telegraph is in Donetsk - he says it's difficult to know exactly what is happening:
