Two suspects identified in Boston bombing

US authorities have identified two suspects who may be responsible for the Boston bombings.

Investigators in white jumpsuits work the crime scene on Boylston Street following the bomb attack at the Boston Marathon April 16, 2013 in Boston, Massachusetts. Picture: AFP.

BOSTON - United States (US) investigators said on Wednesday they have identified two possible suspects believed to have been involved in the twin bombings at the Boson Marathon on Monday.

The two men were seen near the finish line moments before the bombs exploded.

Former Federal Bureau of Investigation (FBI) Assistant Director Tom Fuentes said it was critical authorities made a breakthrough in the case.

"If by some chance they're not involved in the bombing they're certainly prime witnesses."

CNN has reported that a circular sent out on Wednesday to federal and state law enforcement agencies features photos of the two men, to try and identify them.

One of the men is seen carrying a black backpack and authorities believe the bombs may have been placed inside.

The bombings left three people dead and about 180 injured.

Meanwhile, US President Barack Obama is due to visit Boston on Thursday where the close-knit city is still reeling from the twin bombings.

Obama will attend an interfaith memorial at a church a few blocks away from where the bombings occurred.

He lauded the first responders and heroism of those who ran to the help of those injured.

At the same time he condemned the perpetrators.

He said whoever was behind this 'act of terror' would be brought to justice.

At the service he will address the victims and survivors and a country on edge, shaken by an act that came without warning.