WASHINGTON (AFP) - The Pentagon is clamping down on troops' use of fitness trackers and phone apps that allow a user's location to be tracked, officials said Monday (Aug 6), after it emerged that sensitive data was ending up online.

Effective immediately, troops and Defense Department personnel working in certain operational areas such as war zones are prohibited from using GPS features on any government or private gear.

The move to increase troop security comes in part as a response to exercise-logging company Strava publishing a map compiling its users' activity.

In Iraq and Syria, viewers could easily spot beacons of activity in remote places where military bases are located, presumably indicating favorite jogging or walking routes.

"These geolocation capabilities can expose personal information, locations, routines and numbers of Department personnel, and potentially create unintended security consequences and increased risk to the joint force and mission," Deputy Defense Secretary Patrick Shanahan said in a memo.

Commanders will still have the discretion to authorise the use of GPS devices and apps based on mission requirements and risks to operational security.

Troops in areas where security is less of a concern, such as bases in the US or at the Pentagon itself, can still use their GPS-equipped devices and apps in most cases.