The Boston bomber has apologised

Dzhokhar Tsarnaev, the 21-year-old behind the 2013 Boston bombing attacks that killed three and injured hundreds, has apologised.

Speaking in court on Wednesday as he was formally sentenced to death, Tsarnaev, who carried out the attacks with his late brother Tamerlan, said: "I am sorry for the lives that I have taken."

"I would like to now apologise to the victims and to the survivors," he said. "Immediately after the bombing, which I am guilty of - let there be no doubt about that - I learned about some of the victims... I learned their stories, their names."

He personally addressed survivors, telling them he was sorry "for the suffering I caused you, for the damage I've done, irreplaceable damage".

"I want to ask forgiveness from Allah," he said. "I pray to Allah to bestow his mercy upon the deceased. I ask Allah to have mercy upon me, upon my brother, upon my family. "

The hearing included emotional impact statements made by victims and their family members.

More: What survivors of the Boston Marathon bombing have to say about the verdict