The FBI special agent Richard DesLauriers on Thursday released the photos and video of two suspects for Monday's deadly bombings in Boston, asking for the public's help to identify them.

Speaking at the news conference in Boston, DesLauriers said it was the "highest priority" for investigators to identify and locate those suspects who might be responsible for the Boston bombings.

He said the images were posted on the agency's website, encouraging the public to provide law enforcement authorities with clues.

The two male suspects were shown in the released images wearing a dark hat and a white hat respectively. One of them was seen placing a bag that was believed to be the one which went off near the Boston Marathon finish line.

Earlier on Thursday, US President Barack Obama joined and spoke at a memorial service in the city of Boston to honor the victims of the bombings.

"We will find you. We will hold you accountable," said Obama, vowing to take those behind the bombings to justice.

Twin explosions occurred on Monday afternoon near the finish line of the Boston Marathon, killing three people and wounding over 170 others.

The authorities have approached the Boston bombings as an "act of terror," but the motives and perpetrators remain unknown.