The District stepped up security Monday in response to a pair of deadly explosions at the finish line of the Boston Marathon as local residents waited to hear from loved ones who had taken part in the race.

"My coach and one of my teammates was up there -- they're both OK," said Frank DeVar, who manages the Pacers running store in Logan Circle. "I'm just hearing back from people nonstop. I think that's what a lot of people here are doing."

The DC and Montgomery County Road Runners clubs posted messages on their websites saying neither had heard of any injuries to members.

"That does not mean that everything is OK," DC Road Runners President Brian Danza wrote. "Please pray for those who were hit by this horrifying attack."

There were 171 runners from D.C. taking part in the marathon, along with 448 from Maryland and 654 from Virginia.

In the District, Pennsylvania Avenue was shut down near the White House as police increased their presence in Metro stations and around the city.

"We're keenly aware of the potential consequences of these kinds of terrorist acts," Mayor Vincent Gray said, adding that there were no specific threats to Washington.

Tuesday's Emancipation Day festivities, which include a parade, fireworks, concerts and speeches, will go on as scheduled, Gray said, though security will be increased.

"We feel very comfortable it's going to be a safe event," D.C. Police Chief Cathy Lanier said. "Come down and enjoy."

Prince George's County police increased security at critical infrastructure, while Baltimore police said they moved to a state of heightened awareness.

Outside the White House, about a dozen police officers stood watch as tourists took their photos from behind the barricade tape. Many were unaware of what had transpired in Boston.

"We wanted to take pictures in front of the gates, but they blocked everything off," said Adonay Peraca, who had come in from Centreville, Va. "Now we're all just standing here."

On Capitol Hill, House Speaker John Boehner called for a moment of silence on the House floor after a brief and emotional floor speech by Rep. Michael Capuano, whose district includes the Boylston Street area where the explosions occurred. "Today in Massachusetts it is a state holiday called Patriots Day," he said. "We remind ourselves what it is to be an American, what it is to be a patriot, what it is to be a society that cares for each other." When the votes for the day ended, a few more lawmakers gave short speeches in tribute to Boston. Rep. Ted Poe, R-Texas, said whoever caused the explosions, "must be brought to justice, because justice is what we do in this country and that is just the way it is."

President Obama addressed the nation just after 6 p.m.

"The American people will say a prayer for Boston tonight," he said. "Any responsible individuals, any responsible groups, will feel the full weight of justice."

Obama cautioned people about jumping to conclusions before investigations could be completed.

"We still do not know who did this or why," he said. "Make no mistake -- we will get to the bottom of this."

Staff writers Susan Ferechio and Brian Hughes contributed to this report.