(Updates with details, quotes from police; adds byline)
By Drew Singer
PHILADELPHIA, Dec 21 (Reuters) - A man with a pistol fatally shot three people on Friday in rural western Pennsylvania, one of them in a church, before he was killed in a shootout with state troopers as he tried to flee in a pickup truck, authorities said.
Three state troopers also were injured in their confrontation with the gunman in Frankstown Township, about 100 miles (160 km) east of Pittsburgh, shortly after 9 a.m. EST (1400 GMT), state police said.
The violence in Pennsylvania unfolded as bells tolled and many Americans were observing a moment of silence for the 20 children and six adults shot to death one week ago by a gunman at an elementary school in Newtown, Connecticut.
The Newtown shooter, 20-year-old Adam Lanza, also shot his mother to death at their home before going on his rampage, which ended with his suicide and has reignited a national debate over gun control.
The National Rifle Association pro-gun lobby marked the occasion on Friday with a statement urging that armed guards be placed at the nation's schools to improve security.
Friday evening, investigators were still piecing together events behind the deadly shootings in Pennsylvania.
"We don't believe it was a domestic dispute, but we also don't know a motive, because the shooter was not related to any of the victims," trooper David McGarvey, a state police spokesman, said hours after the unexplained slayings.
In fairly rapid succession, the gunman shot and killed a woman inside a church, then fatally shot two men at their respective homes - all within a short distance from each other - before trying to flee in his pickup truck.
He opened fire at two state police patrol cars rushing to the scene as he passed them on a two-lane road and slammed head-on into a third patrol car. The gunman was killed in an exchange of gunfire with police at the crash scene, McGarvey said.
The identities the gunman and his victims were being withheld until their next of kin were all notified, he said.
All three troopers involved in the chase were injured - one from the collision, one hit in the face by bullet fragments and shattered glass, and one who was shot in the chest but survived thanks to a bullet-proof vest. All three were treated and released from a local hospital, McGarvey said.
Another state police spokesman, trooper Adam Reed, said earlier it did not appear that the shooting had any connection to events last week in Connecticut, but added, "that's all still being looked into." (Reporting by Drew Singer and Daniel Trotta; Additional reporting and writing by Steve Gorman; Editing by Sandra Maler, Alden Bentley, Gary Hill)