Boston Marathon bomber Dzhokhar Tsarnaev has been formally sentenced to death for the 2013 attacks that killed three people and injured more than 260 others.

The 21-year-old addressed the court for the first time on Wednesday, apologising for the irreparable harm and noting the strength, patience and dignity of the survivors who spoke before him.

A jury had already sentenced him to death in May, but the judge was required to formally do the same. An appeal will follow automatically as required by US law.

"I am sorry for the lives that I have taken, for the suffering that I have caused you, for the damage that I have done, irreparable damage," said the ethnic-Chechen college student.

"I pray for your relief, for your healing."

His five-minute speech included religious references and praise to Allah. He paused several times, looking as if he was trying to remain composed.

The apology came after Tsarnaev listened for about three hours as victims and their loved ones criticised him for his "cowardly" and "disgusting" acts.


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Rebekah Gregory, a Texas woman who lost a leg in the bombing, told Tsarnaev: "While your intention was to destroy America, what you have really accomplished is actually quite the opposite - you have unified us."

"As long as your name is mentioned, what will be remembered is the evil you've done," US District Judge George O'Toole told Tsarnaev before sentencing him to death by lethal injection. "What will be remembered is that you murdered and maimed innocent people and that you did it wilfully and intentionally. You did it on purpose."

Tsarnaev and his older brother, Tamerlan, carried out the double bombing at the Boston Marathon finish line, one of the deadliest attacks on US soil since the September 11, 2001 attacks.

The two pressure-cooker bombs, hidden in backpacks, killed three people and wounded 264 others, including 17 who lost limbs.

The brothers went on the run and killed a police officer, before Tamerlan was shot dead and Tsarnaev arrested, four days later.

He was found injured in a grounded boat on which he had scrawled a bloody message defending the attacks as a means to avenge US wars in Iraq and Afghanistan.

Source: Reuters