The surviving suspect in the Boston Marathon bombings was today charged with conspiring to use a weapon of mass destruction and could face a death sentence.

US Attorney General Eric Holder in a statement detailed the charge against 19-year-old Dzhokhar Tsarnaev, who is listed in a serious but stable condition.

Tsarnaev made his first appearance before a magistrate judge in Beth Israel hospital, according to Gary Wente, circuit executive of the 1st US Circuit Court of Appeals.

Officials said Tsarnaev and his older brother and suspected co-conspirator, Tamerlan, set off the twin explosions at last Monday’s marathon, killing three people and injuring more than 180 others.

The White House said Tsarnaev will not be tried as an enemy combatant in a military tribunal because he is a naturalised US citizen.

The Tsarnaev brothers were born in sourthern Russia. White House spokesman Jay Carney said Dzhokhar will be prosecuted in the federal court system.

Dzhokhar Tsarnaev remained unable to speak with a gunshot wound to the throat.

He is expected to face separate state charges in the fatal shooting of a university police officer.

Seven days after the bombings, the city planned to mark the traumatic week with mournful silence and a return to its bustling commute.

Massachusetts governor Deval Patrick has asked residents to observe a moment of silence at 2.50pm local time when the first of the two bombs exploded near the finish line.

Bells will ring across the city and state after the minute-long tribute to the victims. The White House said President Barack Obama would observe the moment of silence. privately.

Tsarnaev was discovered on Friday night hiding in a boat covered by a tarpaulin in suburban Watertown. His brother was earlier killed during a shoot-out with police in an escape bid.

The motive of the two ethnic Chechen brothers remains unclear. A private funeral was scheduled today for Krystle Campbell, a 29-year-old restaurant worker killed in the blasts.

A memorial service will be held tonight at Boston University for 23-year-old Lu Lingzi, a graduate student from China.

The parents of Tamerlan Tsarnaev insisted that he came to Dagestan and Chechnya last year to visit relatives and had nothing to do with the militants operating in the volatile part of Russia.

His father said he slept much of the time. A lawyer for Tamerlan Tsarnaev’s wife said that federal authorities have asked to speak with her.

Attorney Amato DeLuca said Katherine Russell Tsarnaev did not suspect her husband of anything, and that there was no reason for her to have suspected him.

He said she had been working 70 to 80 hours, seven days a week, as a home health care aide. While she was at work, her husband cared for their toddler daughter, he said.

Doctors said today that all of the more than 180 people injured in the blasts now seem likely to survive.

As of today, 51 people remained in hospital, three of them in a critical condition and five listed as serious.

At least 14 people lost all or part of a limb; three lost more than one. Two children with leg injuries remain at Boston Children’s Hospital.

A seven-year-old girl is in critical condition and 11-year-old Aaron Hern is in fair condition.

Meanwhile, surgeons at a Cambridge hospital said the Boston transit police officer wounded in a shootout with the suspects had lost nearly all his blood, and his heart had stopped from a single gunshot wound that severed three major blood vessels in his right thigh.

Richard Donohue (33), was in critical but stable condition. He is sedated and on a breathing machine but has opened his eyes, moved his hands and feet and squeezed his wife’s hand.

AP