Boston has paid solemn tribute to the victims of the marathon bombings, observing a moment of silence and raising the US flag exactly one year after the attacks that stunned the nation.

Vice President Joe Biden led an emotional and highly-charged tribute at the Hynes Convention Center, just steps from the scene of the attack that left three dead and more than 260 others wounded.

“You have become the face of America’s resolve, not unlike what happened on 9/11,” Biden told the survivors, relatives of victims and emergency workers who responded to the carnage on April 15, 2013.

When this year’s marathon takes place on Monday, Biden said it would send a message “not just to the rest of the world but to the terrorists that we will never yield, we will never cower”.

Braving the rain, Biden and Massachusetts governor Deval Patrick led a flag-raising ceremony near the race finish line, where the two pressure cooker bombs exploded last year.

Biden and the crowd bowed their heads for a moment of silence before church bells tolled at 2.49pm, the time when the first bomb exploded.

In Washington, President Barack Obama and his staff observed a moment of silence in the Oval Office, a White House official said.

Obama sent thoughts and prayers to those struggling to recover, and paid tribute to the “incredible courage and leadership of so many Bostonians in the wake of unspeakable tragedy”.

The attacks in the northeastern city of nearly one million were allegedly carried out by two brothers of Chechen descent who had lived in the US for years.

Dzhokhar Tsarnaev, who is now 20, and his 26-year-old brother Tamerlan were identified thanks to pictures and video footage.

Tamerlan died after an exchange of fire with police.

Dzhokhar was wounded and captured, and will go on trial in November.