Video surveillance provided by a U.S. drone and given to the Turkish military was used in a Turkish airstrike that killed 34 civilians late last year, according to Pentagon officials.
The airstrike, meant to hit rebel fighters, sent shockwaves and ignited protests throughout Turkey, which is a NATO ally of the U.S.
The airstrike also raises questions on how U.S. partners use information given to them by U.S. drones.
During a routine air patrol over northern Iraq last December, a U.S. military team monitoring a Predator drone video feed identified a number of people and pack animals moving suspiciously toward the Turkish border with Iraq where Turkey has been battling the outlawed Kurdistan Workers' Party, or PKK.
The U.S. team, working jointly with Turkish military in Ankara, passed the information over to the Turkish officials for analysis, according to Pentagon officials.
Pentagon officials familiar with a U.S. after-action report of the incident said the U.S. was then asked by the Turkish military to move the Predator drone out of the area, no longer assisting the Turkish military with the caravan.
After the U.S. drone left the area, Turkish warplanes moved in and attacked the site. The U.S. drone was out of range to monitor the strike, according to Pentagon officials.
When asked about the incident during a Thursday briefing with reporters at the Pentagon, Pentagon Press Secretary George Little refused to comment on the incident, which was first reported in the Wall Street Journal.
"I won't comment on intelligence-sharing with our Turkish allies, but what I can say is that we have an enduring relationship with Turkey," Little said.
"The importance of counter-PKK efforts is critical, as the secretary indicated in his trip to Turkey, and we will continue to work with Turkey on counter-PKK efforts and on other challenges," he continued.
The United States and Turkey have had a relationship since 2007 to monitor the border with Iraq for guerrilla fighters who frequently attack Turkey from bases inside Iraq's northern Kurdish region.
Both sides have been working together in what is called a "fusion cell," a joint facility in Ankara where the United States supports Turkey in monitoring its border with Iraq.
The decision to send the drone away was made by Turkey, not the United States, according to a Pentagon official.
Pentagon officials said the U.S. military intelligence staff that reported the caravan in the fusion cell could not tell whether the caravan of people and animals were fighters or civilians because everybody was wearing heavy winter gear.
The location of the caravan was suspicious because it was on a route frequented by rebel fighters, officials said.
The Pentagon officials did not know if the United States had been asked by Turkey, prior to striking the caravan, to go back and re-examine the caravan.
The issue of drone flights in Turkey is sensitive for the Turkish government. Turkish requests to buy U.S. drones have faced opposition in Congress. In order to improve relations with Turkey, the United States agreed to set up this relationship to monitor Turkey's border with Iraq.