ANKARA, Turkey — Turkish police believe they have found the body of an American tourist reported missing in Istanbul 12 days ago, a police official said on Saturday.

Sarai Sierra, 33, from New York City, had been traveling alone and was reported missing on Jan. 21.

State-run Anatolian news agency said the body was discovered in the ruins of the old city wall by residents in the low-income Sarayburnu neighborhood and that Sierra's driving license was found on the body.

"[We are] 70 to 80 percent sure the body belongs to her but this is not absolutely certain," an Istanbul police official told Reuters on condition of anonymity, adding more tests needed to be completed.

The news agency said the cause of death had yet to be determined but police were investigating the possibility that Sierra had been killed elsewhere and her body moved to Sarayburnu.

Other Turkish police told The Associated Press that Sierra had suffered a fatal blow to the head.

Istanbul police chief Huseyin Capkin also said Sunday that forensic experts had not concluded their autopsy report, but that it was "clear" the head injury caused her death, AP reported.

NTV, a Turkish broadcaster, says 15 people have been detained for questioning in the case, AP reported.

Sierra, a 33-year-old mother of two, was last heard from on Jan. 21, the day she was to fly home from a vacation. Her body was discovered Saturday evening near the remnants of ancient city walls.