Two flash mobs — one of them comprising more than 100 juveniles — caused pandemonium Saturday night near Philadelphia's Rittenhouse Square, assaulting at least three people and committing a robbery, police said. Two teenagers were arrested by SEPTA police.

The melee began around 7 p.m. Saturday on the 1700 block of Walnut Street and spread to nearby streets, said Philadelphia police, who provided few details Sunday.

In a brief statement, police said one group emerged from a club and assaulted a couple walking on Walnut Street. The club was not identified and police did not provide the age of the couple, the manner of the alleged assault, or whether there were any injuries.

The other group, the juveniles, were "acting rowdy and harassing citizens" in the same block of Walnut Street, according to the police statement.

A SEPTA police officer who was helping Philadelphia police disperse the crowds was punched and kicked by a 16-year-old girl, according to SEPTA spokesman Andrew Busch. He did not release her name, saying only that she is from West Philadelphia and has been charged with assault on police, simple assault, resisting arrest, and related offenses at 15th and Market Streets. It was not clear whether that officer was the third assault victim or a fourth. He was not injured, Busch said.

Also arrested was a 14-year-old boy from Southwest Philadelphia. Busch said a SEPTA officer saw him punching a person in the crowd around 15th and Market. When the officer intervened, the teenager resisted, Busch said. He has been charged with simple assault, resisting arrest, and related offenses, Busch said.

Both teens were handed over to the Philadelphia Police Department for processing, Busch said. It could not be determined whether they remained in custody.

No details were provided by Philadelphia police on the reported robbery.