An off-duty Philadelphia police officer shot and killed a robbery suspect in the Ogontz section of the city Saturday afternoon, police said.

Police said the incident took place about 2:20 p.m. in the 5700 block of Park Avenue, near Broad and Chew Streets.

The officer, who was not immediately identified, saw a man "armed with a handgun and robbing an elderly citizen," according to a statement by Officer Tanya Little, a police spokeswoman.

The statement gave the following account:

"The officer identified himself as police and ordered the male suspect to drop his weapon. The male pointed his weapon at the officer at which time the officer discharged his weapon," and the suspect ran away.

The officer followed, chasing on foot. "During that foot pursuit, the male pointed his gun again at the officer and fired, at which time the officer returned fire," according to the statement.

The two kept running, until the suspect "collapsed at the corner of Broad and Chew," in front of a T-Mobile store. He was taken to Einstein Medical Center, where he was pronounced dead at 3:06 p.m. The officer was not injured.

Police Homicide and Internal Affairs units are investigating. In the meantime, the officer will be placed on desk duty, according to police, which is routine for police-involved shootings.

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Staff writer Joseph DiStefano contributed to this article.

This story has been updated. An earlier version listed an incomplete sequence of events.