NEW YORK (AFP) - Two more friends of convicted Boston bomber Dzhokhar Tsarnaev were jailed on Friday for impeding the FBI investigation into one of the deadliest attacks on US soil since 9/11.

A US judge sentenced Azamat Tazhayakov, a student from an affluent family in Kazakhstan, to 3 1/2 years for obstruction and conspiracy.

He was convicted in July last year and faces deportation after serving his sentence. He has already spent more than two years in custody.

In a separate hearing, Robel Phillipos, the son of an Ethiopian immigrant, was sentenced to three years for lying to the FBI.

Phillipos, who graduated from high school with Tsarnaev in 2011, confessed at the end of a fifth interview with the FBI to watching a third friend remove evidence from the room.

That friend, Kazakh student Dias Kadyrbayev - who was enrolled at the University of Dartmouth, Massachusetts - was sentenced to six years on Tuesday for obstructing justice.

The April 15, 2013 bombings at the Boston Marathon were among the deadliest in the United States since the September 11 Al-Qaeda attacks in New York, and sowed terror throughout the city.

Shortly after the Federal Bureau of Investigation released images of the suspects to the public on April 18, Kadyrbayev and Tazhayakov went to Tsarnaev's dorm room to remove incriminating evidence.

They took a backpack, tossed it in the garbage and kept a laptop in what prosecutors said was an attempt to protect Tsarnaev while he was on the run.

Tsarnaev had texted the pair after fleeing, saying: "If you want you can go to my room and take what's there." The backpack contained fireworks allegedly used in bomb-making, a jar of petroleum jelly and a thumb drive.

It was recovered by the FBI two days later at a landfill site.

A month earlier, Tazhayakov heard Tsarnaev boast of being able to make a bomb and saying it would be "good to die as a martyr." A jury last month sentenced Tsarnaev to death for the marathon bombings.

His elder brother Tamerlan Tsarnaev, whom the defense argued was the mastermind, was shot dead by police while on the run.