COLOMBO, March 23 (Reuters) - At least 20 Tamil Tiger rebels and three soldiers were killed in a battle in northwestern Sri Lanka on Friday, the military said, as analysts sounded a warning that renewed civil war is spreading. "The LTTE is attacking with mortars ... without considering the safety of the civilians in the area. Three soldiers were killed and 4 injured," military spokesman Brigadier Prasad Samarasinghe said. "We have retaliated to neutralise them and we have observed more than 20 Tiger dead bodies."