Dzhokhar Tsarnaev, in photo released by the FBI, April 19, 2013. (Credit: FBI/AP)

Attorneys for surviving Boston Marathon bombing suspect Dzhokhar Tsarnaev asked a federal judge this week to lift restrictions imposed upon him in prison, arguing they "limit Mr. Tsarnaev's interactions with individuals assisting defense counsel."

Tsarnaev, who is accused of planting an explosives-filled backpack at the feet of an 8-year-old, faces 30 charges, including several terrorism charges that could incur the death penalty, has been held at the Federal Medical Center Devens under special administrative measures, or SAMS, that defense attorneys say are "unlawful and unwarranted." Three people died and more than 260 were injured in the April 15 bombing.

"The government has not alleged that Mr. Tsarnaev has done or said anything since his arrest to commit violence, incite violence or engage in communications that pose a security threat," defense attorney William Fick wrote in his motion asking the court to vacate the SAMs.

A spokeswoman for Carmen Ortiz, the US attorney in Boston, declined to comment, but prosecutors and the FBI said previously that the special restrictions were warranted because of "Tsarnaev's proclivity for violence."

The SAMs restrict Tsarnaev's visitors, phone calls and mail. For example, "He can send no more than one letter, comprised of no more than three double-sided pages, to one adult recipient per week," according to court records. The provisions also keep him isolated and largely confined to a small cell.

Defense attorneys argued in court papers that "there is insufficient factual basis to justify imposition of any SAMs" and they said the provisions "have a dramatic chilling effect on the defense teams' ability to prepare a thorough and vigorous defense."