No arrests have been made in any of the robberies.
"They are a very dangerous group of individuals that are committing armored car robberies in this area," Richard Ross, the assistant special agent-in-charge of the Phialdelphia FBI office, said yesterday.
"This is a top priority for the FBI and the Philadelphia Police Department," he said. "There is a siege on armored cars in the area."
The latest heist unfolded about 10:15 a.m. yesterday at the First Pennsylvania Bank branch at 61st Street and Woodland Avenue.
A Brinks armored car pulled up with about $125,000 in cash and checks to be delivered to the bank.
The Brinks driver, identified by police as Charles Gray, 50, waited in the car while another guard, Ronald Johnson, 27, went inside the bank with a canvas bank bag of money. He was armed with a .38-caliber revolver, police said.
Johnson was in the lobby area, heading for the vaults with a money bag, when a man came up to him and put a gun to his stomach.
Without saying a word, the man took the bag and the guard's revolver. He left the bank with a second man, also armed, police said.
Waiting for them outside was their getaway car, a 1976 Chevy Nova, with a driver.
The men took off through the parking lot outside the bank, then drove west on Paschall Avenue to Felton Street, where they abandoned the car.
Waiting for them there was another getaway car, a blue Cadillac with a white roof and a driver, police said. The men drove off, nearly striking a pedestrian who - according to Ross - angrily wrote down a partial license plate number and called police.
Both cars were later recovered. The Cadillac was found about a mile from the scene, at Lindenwood Street and Greenway Avenue.
Police and FBI agents were combing the area, seeking more detailed descriptions of the four suspects.
The descriptions of the two armed men in the bank match the descriptions given in the other robberies, according to the FBI.