Three federal law enforcement officials, speaking on condition of anonymity, acknowledged that the FBI was responsible for the bugs but refused to comment on whether the Democratic mayor is a target of an investigation or to provide any details about the nature of the probe.
The devices were found Tuesday during a routine sweep of Street's office by police. Street is locked in a bitter rematch against Republican businessman Sam Katz, and the campaign has been marked by charges of threats and race-baiting. Election Day is Nov. 4.
The Philadelphia Inquirer reported that the bugs were part of a "wide-ranging probe" of corruption at City Hall.
Street's administration has faced a series of charges of wrongdoing, according to The New York Times, involving forgiving parking violations by allies, a multimillion dollar contract that was awarded to a firm connected to Street's brother and a mayoral aide's alleged threat to a landlord who rented space to the opposing campaign.
The discovery of the listening devices prompted quick moves by federal agents to seize evidence in the case. Federal agents conducted several searches Wednesday, the Inquirer said, and raided a financial firm run by Street allies that had obtained a no-bid city contract.
Pennsylvania Gov. Ed Rendell, a Democrat, and Sen. Arlen Specter, a Republican, were among several politicians who called on the FBI Wednesday to tell the public what it knows about the eavesdropping equipment.
"I think given this extraordinary situation with four weeks to go in the campaign, it is incumbent upon the FBI to say why they planted the device," Rendell said.
FBI spokeswoman Linda Vizi declined to comment on the devices, other than to say they were not connected to campaign espionage.
The U.S. Attorney's office in Philadelphia did not acknowledge responsibility for the bugs but said it had been in touch with Street. "We have stated very clearly to both Mayor Street and his attorney the mayor's status in this matter," spokesman Richard Manieri said Wednesday night.
A spokeswoman for Street did not immediately respond to Manieri's statement. Earlier Wednesday, Street said he did not believe he was the target of an investigation, but he said he did not know for sure and had not been able to get clear answers from federal authorities.
"I would like to know what's up," Street said. "I haven't done anything wrong, and I don't know that anybody in my cabinet or in my staff around me has done anything wrong."
Street's campaign suggested the bugging was instigated by the U.S. Justice Department for political reasons.
"The timing of the discovery of these listening devices seems incredibly strange, seeing that we are four weeks out of the election, and we have a Democratic mayor ahead in the polls, and we are on the eve of the first mayoral debate," Street campaign spokesman Frank Keel said.
"Do we believe that the Republican Party, both at the federal level and state level, is pulling out every stop to get Pennsylvania in 2004? Absolutely," Keel said. "Is the Republican Party capable of dirty tricks? I think that is well-documented."
U.S. Attorney Patrick Meehan, the top federal prosecutor in Philadelphia, declined to say what federal agents might know about the bugs but denied politics plays any role in his office's decisions.
"The U.S. Attorney's office in the Eastern District of Pennsylvania has a long and proud history of doing its work without regard to partisan politics. That was the practice of my predecessors, and it is my practice as well," Meehan said in a statement.
Philadelphia Police Commissioner Sylvester Johnson said he turned the matter over to the FBI. He said the security sweeps of the mayor's office have been going on for decades.
An aide to Street who spoke on condition of anonymity said that more than one microphone was found and that all were within the mayor's office suite. Officials would not say how long the equipment was believed to have been in place, but police said a sweep done in June found nothing suspicious.
Katz called the discovery "breathtakingly shocking." His campaign denied having anything to do with the bugging.
Street beat Katz four years ago by fewer than 10,000 votes in this city of 1.5 million. Polls also show a neck-and-neck race in this year's campaign.
In August, someone tossed what was believed to have been an unlit firebomb through the window of a Katz campaign office. An aide to Street and a former city employee were charged with making threats after getting into a confrontation the same day. Supporters of Street, who is black, and supporters of Katz, who is white, have accused each other of race-baiting.
Also Wednesday, the Katz campaign filed a private criminal complaint accusing Street of refusing to return $125,000 in campaign donations it claimed were improper.