The Federal Bureau of Investigation released pictures and a video showing two suspects wanted in connection to the Boston bombing on Thursday, seeking the public's help in finding them. The footage shows the two men walking on a crowded sidewalk minutes before the bombs exploded near the finish line.

"Today we are enlisting the public's help to identify the two suspects," Richard DesLauriers, the FBI's special agent in charge in Boston, told a news conference.

Both men carried backpacks that were believed to contain the bombs. The man identified as suspect No. 1 wore a dark baseball cap. Suspect No. 2 wore a white cap backwards and was seen setting down his backpack on the ground, DesLauriers said. "Somebody out there knows these individuals as friends, neighbors, co-workers or family members of the suspects. Though it may be difficult, the nation is counting on those with information to come forward and provide it to us," he said while cautioning that they were considered armed and dangerous.

Investigators hoped the men would be identifiable within hours of the release of the pictures and video, a national security official said, speaking on condition of anonymity.

Investigators were looking at the men for some period of time before deciding to make the videos public, and they had extensive video and still pictures to justify the FBI decision to label the two men as suspects, the official said.

At least one other person of interest who featured in crime scene pictures had been ruled out as a suspect. Also ruled out earlier in the week was a Saudi student who was injured in the attacks, the official said.

Some of the victims of the attack suffered gruesome injuries, and at least 10 lost limbs as a result of the blasts. Investigators believe the bombs were made of pressure cookers packed with shrapnel.

U.S. President Barack Obama sought to bring solace to Boston in an interfaith service at a cathedral near the bomb site, declaring "You will run again" and vowing to catch whoever was responsible.

He promised resilience in a message directed toward Boston but also to a country that was on edge.

"As you begin this long journey of recovery, your city is with you, your commonwealth is with you, your country is with you," Obama said. "We will all be with you as you learn to stand and walk and, yes, run again. Of that, I have no doubt. You will run again."

After his speech, Obama met with volunteers and Boston Marathon organizers, many of whom cared for the injured, and with victims at Massachusetts General Hospital.