KIEV, Feb. 1 - The head of NATO warned on Wednesday that Ukraine faced its worst violence "in a long time" as global alarm rang out over a spike in bloodshed that has killed 19 people in the European Union's backyard, AFP reported.

Government forces and Russian-backed separatists exchanged mortar and rocket fire for a fourth day around the flashpoint eastern town of Avdiyivka that sits just north of the rebels' de facto capital Donetsk.