Boston explosion | At least 3 dead, 130 injured in marathon bombing

Two bombs struck near the finish line of the Boston Marathon on Monday, turning a celebration into a bloody scene of destruction.

The death toll had risen to three Monday night. Scores were injured at the scene. One of the dead was an 8-year-old boy, according to a state law enforcement source.

Hospitals reported at least 144 people are being treated, with at least 17 of them in critical condition and 25 in serious condition. At least eight of the patients are children.

At least 10 people injured had limbs amputated, according to a terrorism expert briefed on the investigation.

Several of the patients treated at Massachusetts General Hospital suffered injuries to lower limbs that will require "serial operations" in the coming days. Some injuries were so severe amputations were necessary.

In Washington, President Barack Obama vowed: "Any responsible individuals, any responsible groups, will feel the full weight of justice."

The terrorist attack, near the marathon's finish line, triggered widespread screaming and chaos, shattered windows and barricades and sent smoke billowing into the air at Copley Square.

The blasts were about 50 to 100 yards apart, officials said, on a stretch of the marathon course lined with spectators cheering runners through the final yards of a 26-mile, 385-yard endurance feat.

Allan Panter, a doctor who was near the finish line waiting for his wife to finish the race, said he was standing about 20 to 25 feet from the first blast. He said he treated victims on the street after the explosion.

"I saw at least six to seven people down next to me," he said. "They protected me from the blast. One lady expired. One gentleman lost both his (lower) limbs. Most of the injuries were lower extremities."

Bill Iffrig, 78 and a veteran marathoner, was nearing the finish when "the shock waves just hit my whole body and my legs just started jittering around." Iffrig, who can be seen in video of the explosion wearing an orange tank top, was helped to his feet by an event volunteer and had just a scratch from his fall.

Federal authorities are classifying the bombings as a terrorist attack, but it's not clear whether the origin was domestic or foreign, a federal law enforcement official with knowledge of the investigation said.

A federal law enforcement official said that both bombs were small, and initial tests showed no C-4 or other high-grade explosive material, suggesting that the packages used in the attack were crude explosive devices.

Authorities in Boston found at least one other explosive device that they were dismantling, Boston Police Commissioner Ed Davis said.

One unexploded device was found at a hotel on Boylston Street near the bomb site and another unexploded device was found at an undisclosed location, Keating, a Democrat and member of the House Homeland Security Committee, said. He called the bombing a "sophisticated, coordinated, planned attack."

It was unclear who may have planted the marathon bombs. There were no credible threats before the race, a state government official said.

There is no suspect in custody, but many people are being questioned, Davis said.

Also, a Saudi national with a leg wound was under guard at a Boston hospital in connection with the bombings, but investigators cannot say he is involved at this time and he is not in custody, a law enforcement official said Monday evening.

The unexploded devices that were recovered could provide a treasure trove of information such as fingerprints and indications of the bomb maker's design, and from the bombs that did explode, investigators would be looking for fragments and anything indicating the "signature" of the bomb makers.