Photos of Boston suspects released

The FBI has released photos of two suspects it wants to identify as part of the investigation into Monday's Boston marathon bombings.

CCTV captured the two men, one wearing a dark-coloured baseball cap and the other a white cap, near the scene.

FBI Agent Richard DesLauriers warned members of the public not to approach the two men.

US President Barack Obama earlier vowed at a memorial service for victims the perpetrators would be held accountable.

"We consider them to be armed and extremely dangerous," Mr DesLauriers said of the two suspects, during Thursday evening's press conference in a Boston hotel.

He said the FBI was aware of no additional threat.

Mr DesLauriers warned that the only the photos released by the FBI should be used as credible when the public is considering offering tips.

The agency's website crashed within moments of the photo's release.