ISTANBUL (Reuters) - 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 travelling alone and was reported missing on January 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 licence 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.

Anatolian 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.

"Investigations are still continuing and police officials are still in the field," a second police official said.

(Writing by Seltem Iyigun; Editing by Jason Webb)