From http://www.wired.com/news/conflict/0,2100,47739,00.html
"We have demonstrated the ability to selectively deny GPS signals on a regional basis, particularly ... when our national security is threatened," said Lt. Jeremy Eggers, a spokesman at Schriever Air Force Base in Colorado. That's home to the 50th Space Wing ( http://www.schriever.af.mil/50sw/ ), which oversees GPS.
That would mean only military GPS receivers -- in planes, ships and in the hands of U.S. special forces -- would work within the targeted area.
Eggers wouldn't say if a selective denial would be precise enough to hit just Afghanistan, or if neighboring nations like Pakistan and Uzbekistan would be affected too. He'd only say that the "region can be very well defined."
Selective availability (SA), which globally degraded the quality of GPS available to civilians, has been turned off since a May 2000 executive order signed by President Clinton. It's been replaced by selective deniability, which allows the military to geographically pinpoint areas should it choose to degrade GPS quality.
Pentagon Proposes Power Boost in Future GPS Navigation Satellites @ http://www.space.com/missionlaunches/gps_upgrade_020507.html