U.S. military officials now admit an attack on Kandahar airport by unknown gunmen coincided with the departure of the first batch of al-Qaida and Taleban detainees for Cuba.

U.S. officials still maintain the shooting was not related to the detainee transfer.

But they now acknowledge Thursday's attack was the first of its kind since U.S. troops occupied Kandahar airport. They also admit it began about the same time that the first planeload of detainees was leaving - not 15 to 20 minutes after the takeoff as originally reported.

The officials say they believe it was what they term a "probing" assault along the airport's well-guarded perimeter.

But they say despite the curious coincidence of timing, the direction of the firing makes it clear the probe was not aimed at the military transport plane getting ready for departure for the U.S. Naval Base at Guantanamo Bay, Cuba.

The officials say they still have no idea who launched the probe. They say U.S. troops who scoured the area after returning fire found nothing.

No one was injured in the incident.