The FBI has released images and video of two suspects in the deadly Boston Marathon bombings.
FBI special agent Richard DesLauriers said the two men were "armed and extremely dangerous" and warned the public not to approach them.
He said the pictures came from surveillance cameras near the explosion sites. One man sought by police is believed to have planted the devices near the finish line of the race.
Three people were killed and more than 170 others were injured in the twin blasts on Monday.
"Identifying and locating those responsible is now our highest priority.. Someone out there knows these individuals," Mr DesLauriers said.
The images were released hours after President Barack Obama and first lady Michelle Obama attended an interfaith service at a Roman Catholic cathedral in Boston to remember the victims, including an 8-year-old boy.