Thursday's attack on a Pakistani air base near Islamabad by heavily armed militants, which security forces were able to repel, has been followed by the news that gunmen executed about 20 Shiite Muslims today in northern Pakistan.

NPR's Lauren Frayer reports from Islamabad that officials say the attackers stopped three minibuses en route to the city of Gilgit. Officials say they asked all the passengers to show their ID cards, then pulled only the Shiite Muslims off the buses and shot them execution-style.

The attack happened in a remote area made famous by the book Three Cups of Tea, about an American volunteer, Greg Mortenson, who built schools there. It's a poor, rural region where sectarian attacks have happened before.

As Lauren adds, some Sunni Muslim extremists consider Shiites to be heretics, and have staged attacks on them in the past.

As for the attack at the air base, the BBC's M. Ilyas Khan is there and reports that "the search is on for militants who may have escaped." He also notes that "this is the third major attack in about as many years in which militants were able to breach security at a high value military installation." The militants were reportedly armed with guns, grenade launchers and suicide vests.

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