A man who shot and wounded a policeman at point blank range as he sat in his patrol car was inspired by Islamic State militants, police said.
Edward Archer, using a stolen gun, fired at least 11 shots at Jesse Hartnett in Philadelphia.
Despite being shot, Mr Hartnett left his vehicle and was able to return fire, striking the gunman three times.
Mr Archer was arrested within minutes and later confessed to police he did it for Islam, officers told reporters.
"He has confessed to committing this cowardly act in the name of Islam," Police Commissioner Richard Ross said, because he believes "police defend laws that are contrary to Islam".
The 30-year-old from Yeadon, Pennsylvania, told police he pledged allegiance to Islamic State.
But there is no evidence that he was working with anyone else, Mr Ross said.
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