Competing accounts are surfacing from Libya today about who launched an air strike against several rebel tanks and a passenger bus headed west toward the oil town of Brega from Ajdabiyah. The attack killed at least 13 rebel fighters, a doctor in Ajdabiyah tells the BBC.

On Thursday morning, most news outlets ran with claims from rebel fighters that NATO had mistakenly struck opposition forces for the second time in a week. The BBC quoted one Benghazi resident asking, incredulously "NATO, with all the equipment they have--is this the second mistake?" The Associated Press quoted another rebel commander who said the rebels had even marked their vehicles yellow so that NATO could identify opposition forces. NATO, in a press release, said it was investigating the incident, noting that the fierce fighting between Brega and Ajdabiyah has created an environment that "is unclear and fluid with mechanized weapons traveling in all directions."

Later in the day, however, the story shifted, as some sources quoted rebel leaders who claimed it was in fact Muammar Qaddafi's air force that had perpetrated the attack. McClatchy cited one rebel spokesman who said Qaddafi's planes had breached NATO's no-fly zone for the first time since the U.N. authorized military action in Libya, while the BBC revised its story and quoted another rebel spokesman saying that Qaddafi's SIAI Marchetti SF-260 planes had fired on the rebels. The Washington Post explained that rebels had initially blamed NATO because they had "grown so accustomed to the Western alliance controlling the skies that, when the low-flying planes fired ... they assumed the planes belonged to NATO."

McClatchy notes that Thursday's weather in eastern Libya "was windy and there were small sandstorms, conditions that may have kept NATO aircraft from flying," adding that "the assault apparently was carefully coordinated with Gadhafi loyalist ground troops." When the rebels fled from their tanks, Qaddafi's forces pursued them toward Ajdabiyah. Whatever happened, The New York Times says, NATO doesn't emerge looking good. "If the convoy was struck by a NATO aircraft, the events of the day would serve to underscore the lack of coordination between the Western alliance and the Libyan rebels," the Times writes. If the convoy was struck by Qaddafi's aircraft, NATO failed to police its no-fly zone.