President Barack Obama says Monday's bombings along the route of the Boston Marathon were an act of terrorism. Officials say three people died in the explosions and more than 170 were injured.
Obama told reporters at the White House the bomb attack in Boston was a "heinous and cowardly act" and for the first time described it as an act of terrorism.
"Anytime bombs are used to target innocent civilians, it is an act of terror," the president said. "What we do not yet know, however, is who carried out this attack or why. Whether it was planned and executed by a terrorist organization, foreign or domestic, or was the act of a malevolent individual. That is what we do not yet know and clearly we are at the beginning of our investigation."
Watch related video report by VOA's Richard Green
Meanwhile in Boston, federal, state and local investigators briefed reporters at a hotel not far from the scene of the bombings that rocked the city Monday.
The FBI agent in charge of the investigation, Rick Deslauriers, says officials have received “voluminous tips” in connection with the bombings and investigators will follow the trail of evidence wherever it leads.
“This will be a worldwide investigation. We will go where the evidence and the leads take us," Deslauriers announced. "We will go to the ends of the Earth to identify the subject or subjects who are responsible for this despicable crime and we will do everything we can to bring them to justice.”
The FBI as well as state and local authorities continue to interview witnesses and conduct forensic analysis of the crime scene, which was at the finish line for the Boston Marathon, which draws elite runners from around the world.
Investigators are asking the public to come forward with video or still photographs they may have taken around the time of the bombings as they search for clues.
Boston Police Commissioner Ed Davis says investigators are already sifting through numerous video surveillance tapes from businesses in the area.
“It is our intention to go through every frame of every video that we have to determine exactly who was in the area. This is probably one of the most well photographed areas in the country yesterday,” remarked Davis.
Officials say no one has come forward to claim responsibility for the attack. FBI agent DesLauriers would not comment on reports that police have questioned one man in connection with the case and searched a home in the nearby suburb of Revere.
Massachusetts Governor Deval Patrick said an earlier report that unexploded devices had been found was incorrect. He said the only explosives found were the two that went off.
Patrick urged Bostonians to cooperate with law enforcement authorities.
“Everyone should expect continued, heightened police presence and everyone should continue to personally be vigilant,” he said.
Patrick said an interfaith prayer service is being organized for Wednesday in Boston in the wake of the tragedy.
Longtime Boston Mayor Tom Menino also said the tragedy will bring the city together.
“This is a bad day for Boston, but I think if we pull together we will get through it. We are a strong city and lot of people are willing to work together to make this a better place for all our people,” Menino reassured Bostonians.
The marathon traditionally is held on what is known as Patriot’s Day in Massachusetts, a state holiday that commemorates the first battles of the American Revolution in Concord and Lexington in 1775.
In this image from video provided by WBZ-TV, spectators and runners run from what was described as twin explosions that shook the finish line of the Boston Marathon, April 15, 2013.
An emergency responder and volunteers, including Carlos Arredondo in the cowboy hat, push Jeff Bauman in a wheel chair after he was injured in an explosion near the finish line of the Boston Marathon April 15, 2013.
Medical workers transport the injured across the finish line during the 2013 Boston Marathon following an explosion, April 15, 2013.
Medical workers aid injured people at the finish line of the 2013 Boston Marathon following an explosion, April 15, 2013.
One of the blast sites on Boylston Street near the finish line of the 2013 Boston Marathon is investigated by two people in protective suits in the wake of two blasts in Boston April 15, 2013.
Runner John Ounao cries when he finds friends after several explosions rocked the finish of the Boston Marathon, April 15, 2013.
A police officer clears Boylston Street following an explosion at the finish line of the 2013 Boston Marathon, April 15, 2013.
Medical workers aid a wounded woman at the finish line of the 2013 Boston Marathon following two explosions there, April 15, 2013.
Medical workers aid injured people at the finish line of the 2013 Boston Marathon following an explosion in Boston, April 15, 2013.
A woman is comforted by a man near a triage tent set up after explosions went off at the 117th Boston Marathon, April 15, 2013.
A Massachusetts state police officer guards the area containing the medical tent, rear, following an explosion at the 2013 Boston Marathon, April 15, 2013.
An unidentified Boston Marathon runner leaves the course crying near Copley Square following an explosion, April 15, 2013.
A Boston police officer wheels in injured boy down Boylston Street as medical workers carry an injured runner following an explosion during the 2013 Boston Marathon, April 15, 2013.
Justine Franco of Montpelier, Vermont, holds up a sign near Copley Square looking for her missing friend, April, who was running in her first Boston Marathon, April 15, 2013.
President Barack Obama leaves the podium after speaking in the press briefing room at the White House, April 15, 2013, following the explosions at the Boston Marathon.
Security has been boosted in several major U.S. cities, including New York and Washington, and condemnations of the Boston bombings have come from around the globe.