New York (AFP) - Boston bomber Dzhokhar Tsarnaev filed a motion Monday demanding a new trial, less than two weeks after he was sentenced to death for attacking the city's marathon in 2013.

The preliminary motion did not stipulate grounds for a new trial, other than to say it was "required in the interests of justice."

His lawyers said it was a "placeholder" motion that would be expanded upon by August 17.

Tsarnaev, 21, apologized to his victims for the first time during a highly emotional court hearing in Boston on June 24 when he was sentenced to death on six counts for the April 15, 2013 bombings.

A US jury determined the sentence unanimously on May 15 after finding him guilty on all 30 counts related to the bombings, the murder of a police officer and other crimes carried out while on the run.

The bombings killed three people and wounded 264 others in one of the deadliest attacks on US soil since the September 11, 2001 attacks.

They were carried out by Tsarnaev and his older brother Tamerlan, who was shot dead by police while on the run.