Dzhokhar Tsarnaev, 19, the prime and only surviving suspect in the deadly Boston Marathon bombings has been transferred from hospital to prison in fair condition.

US Marshals Service said the young man had been moved from the Beth Israel Deaconess Medical Center to a facility at Fort Devens, Massachusetts, 40 miles (65km) west of Boston.

He has been in hospital with a serious throat wound since his capture following a huge police operation a week ago.

The facility, on the decommissioned Fort Devens US Army base, treats federal prisoners who require specialized long-term medical or mental healthcare.

Meanwhile, a driver allegedly carjacked by the suspects at gunpoint has told how he thought he was going to die.

In an interview with the Boston Globe, a 26-year-old Chinese businessman has told the harrowing experience of being carjacked by Dzhokhar's older brother Tamerlan, 26, several days after the attack on the marathon.

New York police said on Thursday the Tsarnaev brothers had made a spur-of-the-moment plan to drive the hijacked car to Times Square and detonate their remaining explosives: a pressure cooker device and five pipe bombs.

Meanwhile, the Bulgarian online news agency Dnevnik quoted the Associated Press in reporting the suspects' mother, Zubeidat Tsarnaeva, has been added at the CIA's request to a US terrorist watch list 18 months ago.

Tamerlan had also been added to the list, after Russian officials warned the US authorities he may have become radicalized.

"It's all lies and hypocrisy," Tsarnaeva continues to insist.

The Tsarnaevs have Chenen roots.

Dzhokhar has told the investigators the US wars in Afghanistan and Iraq were the motivating factors behind the attack

The twin Boston Marathon bombings killed 3 people, but the number of the injured has risen to 264 from the previous 170, as more people have checked in the hospitals, including the Fort Devens facility, over persisting problems. Some of the wounded had to have their legs amputated.