In addition to key stations, Williams said the beefed-up presence also included trains, buses and trolleys. As a precaution, the agency's K-9 team was used to look for suspicious packages and station announcements were used to encourage passengers to report any suspicious activity.
Williams said the heightened security would continue until officials learned more details about Monday's incident.
"Until we feel comfortable with that information we will continue to have an increased presence and to be extra vigilant," she said.
Nutter said the Broad Street Run on May 5 is expected to continue as planned. The city will evaluate what happened in Boston as details become available, he said, and provide a "much more visible" security presence at the event, which has 40,000 participants signed up so far.
"In light of [Monday's] events in Boston, let me assure you that we will step up our security efforts and response to the Boston Marathon," Nutter said, flanked by top public-safety officials at a City Hall news conference. "Runners and spectators will, in fact, see a much more visible security presence on race day for the Broad Street Run."
He added that city officials would remain on alert for any upcoming public events.
"We will also take necessary precautions and learn from whatever it is that has gone on in Boston in terms of the actual incident. Where were these devices placed? Hopefully we will [have more information] on who did what, how they got there and all of those kinds of details," he said. "And then we'll make the right and appropriate and safe decision for that particular event or any other event that's scheduled in the upcoming weeks here in Philadelphia."
Philadelphia law-enforcement officials will have their hands full with several high-profile events over the next few months. In addition the Broad Street Run, the city will hold its annual Fourth of July fireworks show on the Benjamin Franklin Parkway and host the second Made in America music festival on Labor Day weekend.
Nutter said residents should alert law-enforcement agencies or the city if they see something suspicious. The Philadelphia police tip line is 215-686-8477. Residents can also call 9-1-1 or 3-1-1.
On Twitter: @SeanWalshDN