A bicyclist has been sexually assaulting women in dresses as he rides past them in Center City and South Philadelphia, police say - and as word spread Wednesday, another possible victim came forward.

Special Victims Unit Capt. Mark Burgmann said police received four reports from Aug. 6 to 13 from women ages 24 to 42 who said they were groped under their dresses by a man as they walked on sidewalks in the two sections of the city.

In three of the cases, the alleged groper was on a 10-speed bicycle. In the fourth, the man was on foot, but Burgmann said police believe it is the same assailant, based on the description of the offender and his actions.

In each case, the man did not say a word, Burgmann said.

"During these assaults, our victims are wearing dresses and the offender comes up behind them on his bicycle, reaches up under their dress, and sexually assaults them," he said. "They happen extremely quickly. Most of the victims at first don't even realize what's happening."

Wednesday morning, police released surveillance video showing the man in one of the attacks. Later, at an afternoon news conference at SVU headquarters, Burgmann said police had heard from a fifth woman who had seen news coverage of the first four assaults and believed she was a victim of the same attacker.

Burgmann urged any other victims or witnesses to come forward. He said the women who had spoken to police were shaken.

"They were in shock, they were very upset," he said. "They were just stunned it happened so fast."

He said that after the attacks, one woman sat on nearby steps and cried, whereas another fought back and punched the offender.

"I wouldn't recommend that," Burgmann said. "I would recommend getting away as fast as you can."

Police are concerned that the suspect could step up his attacks.

"There's always a concern that they could escalate," Burgmann said. "He's pretty brazen, as you can see."

The suspect is a 5-foot-4 to 5-foot-6 Hispanic man in his early 20s with a stocky build, according to police. In several of the assaults, he had a backpack that one victim described as black with orange sides.

The confirmed incidents of assault include:

Aug. 6, about 1 a.m., 1800 block of South 15th Street.

Aug. 10, about 10:15 p.m., 900 block of Lombard Street.

Aug. 13, about 12:10 a.m., 700 block of South Eighth Street.

Aug. 13, about 2:30 a.m., 2000 block of South 13th Street.

Tipsters can call 215-686-8477 (TIPS) or send a text message to 773847 (PPDTIP).