Unknown shooter kills US state trooper in ambush

A US state trooper has been shot and killed and another was wounded in an ambush outside a police barracks in Pennsylvania, authorities have said.

State Police Commissioner Frank Noonan said whoever carried out the attack at the Blooming Grove Barracks in Pike County, eastern Pennsylvania, was still at large.

"I know a lot of people are wondering, is the threat resolved? It is not," Noonan said.

"The individual who perpetrated this heinous crime is still at large. We do not have a description or any information on their identify. We are following a number of leads right now."

Noonan described the attack as an ambush that occurred around 10:50 pm (0250 GMT Saturday).

He said police from the neighboring states of New York and New Jersey had provided the state with helicopters.

"It is of a grave concern to us and we are putting every resource available to the Pennsylvania state police or law enforcement in Pennsylvania in action," he said.

The names of the victims have not been released.