BOSTON (REUTERS) - Two college friends of accused Boston Marathon bomber Dzhokhar Tsarnaev pleaded not guilty on Tuesday to charges of obstruction of justice and conspiracy for removing evidence from Tsarnaev's dormitory room three days after the attack.

The two students, who are from Kazakhstan, are accused in federal court of removing a backpack containing fireworks and a laptop computer from Tsarnaev's room at the University of Massachusetts Dartmouth as the FBI was searching for him.

Dias Kadyrbayev and Azamat Tazhayakov, both 19, could face 25 years in prison or deportation if convicted.

An attorney for Kadyrbayev said his client cooperated with investigators from the moment they approached him, turning over Tsarnaev's computer and telling the FBI where it could find the backpack.

"Dias comes from a former Soviet-bloc region where police routinely are distrusted," attorney Robert Stahl told reporters. "Yet when authorities first approached him, he fully cooperated and for nearly 12 hours over two days Dias answered the FBI's questions without an attorney or a Kazakh consular official present."

Tsarnaev, 20, is accused of setting off a pair of homemade pressure-cooker bombs at the race's crowded finish line on April 15, killing three people and injuring 264 in one of the worst attacks on United States (US) soil since Sept 11, 2001.

He is also charged in the death of a university police officer from whom he and his older brother, Tamerlan, tried unsuccessfully to steal a gun, according to authorities.

Kadyrbayev and Tazhayakov were led into the courtroom handcuffed and dressed in orange prison uniforms and white sneakers. They smiled and nodded to family members seated in the courtroom.

REMOVING EVIDENCE

Each is charged with removing evidence including the backpack with fireworks from Tsarnaev's room in an effort to protect him three days after the attack, when the FBI released still images of the Tsarnaev brothers at the site of the bombing.

That FBI release - a call for the public's help in identifying the suspects - panicked the brothers. Their attempt to flee ended in a late-night gunfight with police in the suburb of Watertown on April 18 in which Tamerlan Tsarnaev was killed.

After a day-long manhunt, police found Dzhokhar Tsarnaev hiding in a boat parked in the backyard of a home.

The bag was dropped in a dumpster outside the New Bedford, Massachusetts, apartment where the pair lived. Investigators later recovered it from a landfill.

Tazhayakov's attorney, Arkady Bukh, said his client had not given Kadyrbayev consent to throw the bag away.

Neither is charged with involvement in the bombing.

Mr Stahl said he hoped Kadyrbayev would be acquitted and allowed to return to his family in Kazakhstan.

The two have been in federal custody since May 1, when lesser charges of conspiracy were filed against them. They were indicted on the obstruction-of-justice charges on Aug 8.

A third friend, Robel Phillipos of Cambridge, Massachusetts, is engaged in talks with prosecutors aimed as settling a charge of making false statements in a terrorism investigation.

Tazhayakov's father, Mr Amir Ismagulov, told reporters through a translator his son was "shocked" at the bombing but had become a scapegoat.

Mr Ismagulov, who said he owned oil fields in Kazakhstan, said his son had intended to study petroleum engineering in Texas after he finished his studies in Massachusetts.