The Boston Marathon bombing suspect has been charged in his hospital bed with using a weapon of mass destruction.

Dzhokhar Tsarnaev, 19, an ethnic Chechen college student suspected of carrying out the attacks with his older brother, remains in a Boston hospital under armed guard.

The White House has said the teenager will not be treated as an "enemy combatant" and will be prosecuted through the US criminal justice system.

He has also been charged with one count of malicious destruction of property resulting in death.

The US Department of Justice said, if convicted, Mr Tsarnaev will face the death penalty or life imprisonment.

He was unable to speak after he was captured with throat injuries sustained during shoot-outs with police.

Police declined to comment on media reports he was communicating with authorities in writing.

"There have been widely published reports that he is (communicating silently). I wouldn't dispute that, but I don't have any specific information on that myself," Boston Police Commissioner Ed Davis told CNN.

"We're very anxious to talk to him and the investigators will be doing that as soon as possible."

The FBI said this morning that Mr Tsarnaev remained in a serious condition at Beth Israel Deaconess Medical Center.

Three people died when twin bombs exploded at the finish line of the Boston Marathon last Monday.

A police officer at MIT was shot dead during the search for the Tsaranaev brothers.

A total of 176 people were wounded in the blasts and ten of the injured lost limbs.

The city paid tributes to the dead after a week of blasts, shootouts, lockdowns and one of the largest manhunts in US history.

A minutes silence was held at 2.50pm (7.50pm Irish time) to mark the moment a week ago when the two bombs made of pressure cookers and packed with nails and ball bearings tore through the crowd watching runners complete the Boston Marathon.

Memorial services also took place for two of those killed in the bombings: Krystle Campbell, a 29-year-old restaurant manager, and Chinese graduate student Lingzi Lu.

An eight-year-old boy, Martin Richard, was also killed in the blast.

The city of Boston crawled back to normal today, but the crime scene around the blasts is still closed.

Capture ended massive manhunt

The capture of Mr Tsarnaev on Friday night ended a manhunt that virtually shut down greater Boston for some 20 hours.

His older brother, Tamerlan Tsarnaev, 26, died after a gunfight with police early Friday morning.

Police said the Tsarnaev brothers made enough additional bombs for them to believe that more attacks were planned.

They were also armed with handguns.

A shootout with police in the Boston suburb of Watertown early Friday morning left more than 200 spent shell casings in the street.

Neither Tsarnaev brother was licensed to own guns in the towns where they lived, Cambridge, Massachusetts, authorities said yesterday.

The brothers emigrated to the US a decade ago from Dagestan, a predominantly Muslim region in Russia's Caucasus.

The men's parents, who moved back to southern Russia some time ago, have said their sons were framed.

Much of investigators' attention has focused on a trip to Russia last year by Tamerlan Tsarnaev, and whether he became involved with or was influenced by Chechen separatists or Islamist extremists there.

Tamerlan Tsarnaev traveled to Moscow in January 2012 and spent six months in Dagestan, a law enforcement source said.

Neighbours in Makhachkala, the region's capital city, said he kept a low profile while visiting there last summer, helping his father renovate an apartment unit.

That trip, combined with Russian interest in Tamerlan communicated to US authorities and an FBI interview of him in 2011, have raised questions whether danger signals were missed.