Police in Philadelphia are investigating a tip that members of a radical group may pose a threat to officers following the ambush of a patrolman in his cruiser last week.

The police department said Sunday evening that someone approached an officer on the street and alleged that the man who attacked Officer Jesse Hartnett "had an affiliation to a group with radical beliefs."

Police say they are working with the FBI to investigate the credibility of the information. They have alerted all department personnel.

Authorities said earlier a man tried to grab the gun of an officer working a detail at the hospital where Hartnett is recovering, but they believe that incident is unrelated to the ambush shooting.

A suspect in Hartnett's shooting has been charged with attempted murder.