A US jury has sentenced Boston bomber Dzhokhar Tsarnaev to death by lethal injection.

Three people were killed and 260 were injured when Tsarnaev, now 21, and his brother placed bombs at the finishing line of the Boston Marathon in 2013.

Tsarnaev is likely to be moved to a federal prison in Terre Haute, Indiana, to await execution, but there could be years of appeals.

Victims sobbed as the sentence was read, but Tsarnaev showed no emotion.

"Now he will go away and we will be able to move on. Justice. In his own words, 'an eye for an eye'," said bombing victim Sydney Corcoran, who nearly bled to death and whose mother lost both legs.

After 14 hours of deliberations, the jury concluded that he showed no remorse and therefore should be put to death.

"The jury has spoken. Dzhokhar Tsarnaev will pay for his crimes with his life,'' said US Attorney Carmen Ortiz.

Tsarnaev was found guilty last month of helping carry out the attack, as well as fatally shooting a policeman.

As a state, Massachusetts ended the death penalty in 1984, but Tsarnaev was tried on federal charges, meaning he was eligible for execution.

Tara McKelvey, BBC News, Boston

Tsarnaev stood next to his lawyer. He tilted his head to the side and shifted his weight from one foot to the other as he heard the clerk read the notes from the jurors.

After the death sentence was announced, he bowed his head.

A juror with gold hoop earrings took a drink from a water bottle. A moment later she started to cry. Another juror touched her to reassure her and to comfort her.

Another juror with dark-framed glasses and a blue shirt cried too. He took off his glasses. He wiped his forehead and wiped his eyes. He bit his lips, distraught.

After the sentence was announced, US Attorney General Loretta Lynch said: "The ultimate penalty is a fitting punishment for this horrific crime and we hope that the completion of this prosecution will bring some measure of closure to the victims and their families.''

But not all of the victims supported the death penalty for Tsarnaev.

The parents of Martin Richard, an eight-year-old boy killed in the blast, wrote an article in the Boston Globe newspaper last month asking the government to not seek a death sentence as it would delay their emotional closure.

The Associated Press news agency reached Tsarnaev's father, Anzor Tsarnaev, by phone in the Russian region of Dagestan on Friday. He moaned after hearing the sentence and hung up.

During the trial, Tsarnaev's defence team admitted that he had played a role in the attacks but said that his older brother, Tamerlan - shot dead by police in the subsequent manhunt - was the driving force.

Lawyers also highlighted his difficult early life. The Tsarnaevs - ethnic Chechens - had lived in the former Soviet republic of Kyrgyzstan and the volatile Dagestan region of Russia, near Chechnya. The family moved to the US in 2002.

But prosecutors argued that Dzhokhar Tsarnaev was an equal partner in the attack, showing the jury a message he wrote on the boat where he was arrested.

"Stop killing our innocent people and we will stop," it read.

Throughout the trial, the jurors heard grisly testimony from bombing survivors. They described seeing their legs blown off or watching someone next to them die.

At the start of the penalty phase, the prosecutors showed jurors a photo of Dzhokhar Tsarnaev raising his middle finger to a jail cell security camera months after his arrest.

"This is Dzhokhar Tsarnaev - unconcerned, unrepentant and unchanged," prosecutor Nadine Pellegrin said.

BBC