American spy drones provided intelligence to Turkey's air force for an errant bombing raid in December that killed 35 civilians instead of Kurdish separatists, a US defense official said Thursday.

Turkish F-16s had launched the air raid on December 29 intending to target Kurdistan Workers' Party (PKK) militants after the drone spotted a group moving toward its sensitive southeastern border at night, according to officials in Ankara.

"We're familiar with the incident," said the US defense official, who spoke on condition of anonymity.

"In this particular case, they (drone operators) did notice a group of people and some pack animals. That information was passed on to the Turks and then our drones departed the area."

The United States has Predator unmanned aircraft based in the country and regularly relays information on Kurdish forces gathered from surveillance flights to Turkey's military.

"We had nothing to do with the air strike, in fact we were not in the area when the strike occurred," the official added.

The American role was first reported by the Wall Street Journal on Wednesday and has grabbed headlines in Turkey.

As US forces withdrew from Iraq last year, the United States moved four Predator drones to Turkey to help Ankara track Kurdish PKK militants.

The botched air strike in December triggered a wave of protests by Kurds who accused the government of carrying out a "massacre."

Clashes between Kurdish rebels and the army escalated late last year.

The PKK took up arms in Kurdish-majority southeastern Turkey in 1984, sparking a conflict that has claimed about 45,000 lives. It is labeled a terrorist organization by Ankara and much of the international community.