NATO initially acknowledged attacking only military vehicles that may have been accompanying the refugees, and even suggested that Serb troops had fired on the refugees when the attack began. The Pentagon later backed away from the latter claim, although the circumstances of the attack remain murky. Coming three days after NATO bombs killed civilians aboard a Serb train stranded on a bridge, the potential "friendly fire" incident will fuel the doubts of those NATO countries urging an end to the bombing campaign. But it didn't stop NATO on Wednesday from launching the heaviest night of attacks on Belgrade since the campaign began. "Military commanders can't be deterred from their mission by incidents like this," says Thompson. "They're part of the risk you take when you go to war."
NATO's bombers in Kosovo have claimed their first "friendly fire" casualties, and the fact that they were ethnic Albanian civilians will raise pressure on the alliance to end its air campaign. The alliance acknowledged Thursday that a bomb was accidentally dropped on a column of cars and tractors Wednesday, killing a number of refugees, but blamed the Serbs for putting the civilians in harm's way. "You can't have mistakes like this without paying a price," says TIME Pentagon correspondent Mark Thompson. "This bombing campaign has a political fuse, and once that fuse is burned out the resolve to continue disappears -- this tragedy will obviously accelerate the burning of that fuse."