Libya’s opposition has thus far held off loyalist militias in Zawiya, a key city 30 miles from Tripoli. But Gaddafi’s mercenaries made another attempt Friday to retake Zawiya, and the clash was bloody: At least 50 people were killed, one witness told Reuters. Thirty of those were civilians, and the city’s hospitals are full of the injured. “They could not find a space for the casualties,” a second witness said. There was also fierce fighting in Ras Lanuf, and police in Tripoli fired tear gas on peaceful protesters and killed those who fell to the ground wounded. On Friday, the U.S. stepped up its humanitarian aid to the country, sending two military planes full of emergency supplies to neighboring Tunisia.