TEHRAN, Iran (AP) — Iranian users of the Signal messaging service say they have lost access to the app on their mobile devices. Users in several neighborhoods in the capital Tehran and at least three other major cities contacted by The Associated Press said Monday that access to the app was blocked gradually beginning in the afternoon. They said they could use the system through virtual private networks, services that shield internet users by encrypting their data traffic. Some still had access through desktop version of the app. State media did not report that the app was blocked and calls to authorities were not immediately returned Monday.