A gunman claiming allegiance to Islamic State militants shot and seriously wounded a Philadelphia police officer, saying he ambushed his patrol car "in the name of Islam," the city's police commissioner said on Friday.

Edward Archer of Philadelphia approached Officer Jesse Hartnett, 33, shortly before midnight and fired 11 rounds, three of which hit the officer in his arm, authorities said.

Police released still images from surveillance video that showed the gunman dressed in a long white robe walking toward the car and firing, eventually getting close enough to shoot at point-blank range through the window.

Hartnett chased Archer, who was arrested by responding officers and later confessed to the attack, police officials told reporters.

"He has confessed to committing this cowardly act in the name of Islam," Ross told a press conference, adding that the 30-year-old assailant also referenced Islamic State militants.

Philadelphia Police Captain James Clark added, "He said he pledges his allegiance to Islamic State, he follows Allah and that was the reason he was called on to do this." Separately, a report in the Wall Street Journal cited an unnamed official who told the publication that the suspect had recently traveled to Egypt and Saudi Arabia.

A top U.S. Muslim advocacy group said it had found no evidence that Archer was an observant Muslim.

FBI Special Agent Eric Ruona said Archer had traveled to Saudi Arabia in 2011 and Egypt in 2012 and those trips were under investigation. There was no indication that Archer had acted with anybody else, he said.

U.S. officials have been on high security alert following a series of Islamic State-linked attacks at home and abroad over the last few months.

In November, gunman and suicide bombers affiliated with Islamic State killed 130 people in a series of attacks in Paris. Last month a married couple fatally shot 14 people in San Bernardino, California, in an attack inspired by Islamic State.