Boston has marked the first anniversary of the marathon bombings, which killed three people and injured 264.

The memorial service featured remarks by survivors of the attack and US Vice President Joe Biden.

Mr Biden sounded a note of defiance in his remarks.

He said events like those at the marathon or the 2001 destruction of New York's World Trade Center and attack on the Pentagon demonstrate the resolve of average Americans.

He added: "We refuse to bend, refuse to change, refuse to yield to fear.

"That is what makes us so proud of this city and this state, what makes me be so proud to be an American. It's that we have never, ever yielded to fear. Never."

About 2,500 invited guests attended the memorial at Boston's Hynes Convention Center.

Following the ceremony, the crowd walked down Boylston Street, the final stretch of the marathon, amid heavy rain and high winds to watch officials raise a US flag at the finish line.

That was the point where a pair of home-made pressure-cooker bombs detonated a year ago, ripping through the crowd of thousands of spectators.

A minute's silence was held this evening at the moment the bombs went off.

Afterwards, churches throughout Boston tolled their bells and ships in the city's harbour sounded their horns.

"You have struggled to get through the good days and the bad," said former mayor Thomas Menino, who stepped down at the end of last year after his sixth term in office.

"I know because so many of you have told me about this year of firsts.

"First birthday without your beloved son, first holiday without your daughter, first July 4 where the fireworks scared you."

Mr Menino, who had been hospitalised at the time of the blasts but responded to the scene against his doctor's orders, praised Boston residents' response to the bombing.

"You are strong at this broken place," said Mr Menino.

"That strength thrives even in the heartaches of today because of the compassion that took over this city."

The attacks, which federal prosecutors have blamed on a pair of ethnic Chechen brothers, killed Martin Richard, 8, Krystle Campbell, 29, and Chinese national Lu Lingzi, 23.

It was the worst mass-casualty attack on US soil since the 11 September 2011 attacks that killed more than 3,000 people.

Three days after the bombings, a Massachusetts Institute of Technology police officer, Sean Collier, 27, was shot dead by the same brothers.

Tamerlan Tsarnaev, 26, was killed following a police shoot-out.

His younger brother, 20-year-old Dzhokhar Tsarnaev, was captured when hiding injured in a boat in a suburban back garden.

He is awaiting trial on charges of using a weapon of mass destruction. Federal authorities are seeking the death penalty.