The bodies of the women were found shortly before 2:00 am (0100 GMT) inside the building in the 10th arrondissement of the French capital.

"The scene leads one to think of an execution, but the investigation will determine the exact circumstances," the source said.

One of the women was 32-year-old Fidan Dogan who worked in the institute's information centre, according to its director, Leon Edart.

The identities of the other two women, who were reportedly Kurdish activists but did not work at the Institute, were not immediately available.

The three were last seen mid-day on Wednesday at the centre, which was found locked by late afternoon, according to Edart.