NATO acknowledged that it may have accidentally killed rebels for the second time in less than a week, but said it wouldn't apologize for it. "The situation in the area is still very fluid, with tanks and other vehicles moving in different directions, making it very difficult to distinguish who may be operating them,” said NATO Rear Adm. Russell Harding, going on to say that they didn't know the rebels were operating tanks. "It is not for us, trying to protect civilians of whatever persuasion, to improve communications with those rebel forces," he added. Meanwhile, the first-ever United Nations ship containing humanitarian supplies arrived at the besieged city of Misrata. The ship, chartered by the World Food Program, contains food and medical supplies for the tens of thousands of civilians trapped by Gaddafi's forces in the rebel-held city.