The FBI has released images of two suspects in the Boston Marathon bombings case which left three dead and over 180 injured.
FBI Agent Richard DesLauriers says the images came from surveillance cameras near the explosion sites shortly before the blasts.
"We consider them to be armed and extremely dangerous," Mr DesLauriers said, asking the public not to approach the men.
He said there is no additional danger that the FBI knows of now.
Monday's blasts killed three and injured more than 180.
The images were released hours after President Barack Obama attended an interfaith service in Boston to remember the victims, including an eight-year-old boy.
Earlier today he promised a grieving Boston to hunt down whoever was responsible for the deadly bombing at the marathon, while investigators focused on a man seen dropping off a bag and walking away from the site of the second of Monday's two explosions.
At an interfaith service honouring the victims, Mr Obama said "there is a piece of Boston in me" as he paid tribute to the city shaken by what he has called an act of terror.
"Every one of us stands with you," he said.
There was a heavy police presence around the city's main Roman Catholic cathedral as residents lined up before dawn, hoping to get one of the roughly 2,000 seats inside.
Streets were blocked off around the Cathedral of the Holy Cross. Among the hundreds in line was 18-year-old Eli Philips. The college student was a marathon volunteer and was wearing his volunteer jacket.
He said he was still shocked that "something that was euphoric went so bad".