US prosecutors say they have charged a Daesh (ISIL) sympathizer with attempted murder in the shooting of a Philadelphia police officer.

Thirty-year-old Edward Archer is accused of ambushing an officer in his squad car shortly before midnight on Thursday in Philadelphia, Pennsylvania.

The suspect is being held without bail, the Philadelphia District Attorney's Office said on Saturday.

Philadelphia Police Captain James Clark said the suspect "stated that he pledges his allegiance to Islamic State [Daesh]."

The police officer was ambushed execution-style while sitting in his marked police car, Philadelphia Police Commissioner Richard Ross said Friday at a news conference.

Ross said the attacker told authorities he was pledging allegiance to ISIL, the terrorist group that controls parts of Iraq and Syria.

The assailant fired about eleven shots through the window of the officer’s car. The officer was struck three times in his left arm and suffered a broken arm.

Law enforcement officers across the US have expressed increasing concerns about ambush attacks in recent years. In 2014, 15 officers were shot and killed in surprise attacks, more than any other type of shooting.

Analysts believe tensions between police and citizens have reached an all-time high in recent years over the use of excessive force by police, particularly against minorities.

Large-scale protests have been triggered around the country against police brutality and racial injustice in the past two years.

The Thursday night attack comes a month after two ISIL sympathizers fatally shot 14 people in the city of San Bernardino in California.