Three more suspects have been taken into custody in the investigation of last month's deadly bombings at the Boston Marathon.
The arrests, which were made on Wednesday and announced via Twitter, were for obstructing the course of justice rather than for being directly involved in the marathon bombings.
Two of the men have been identified as Azamat Tazhayakov and Dias Kadyrbayev, both 19 and from Kazakhstan.
They have been charged with conspiracy to obstruct justice by throwing away a backpack containing fireworks and a laptop computer belonging to Dzhokhar Tsarnaev, one of two brothers suspected of carrying out the April 15 attack.
Al Jazeera's Alan Fisher, reporting from Washington, said it was thought the two men recognised Tsarnaev when images were released after the attack and realised he might be in trouble.
US prosecutors charged a third man, Robel Phillipos, with making false statements to investigators, according to documents filed in federal court.
Three people were killed and more than 260 injured in the bombings that led to an intense manhunt through Boston.
Tsarnaev, 19, who is being held in a prison medical centre, faces criminal charges relating to the attacks.
His older brother, Tamerlan Tsarnaev, 26, died in a gun battle with police officers.
The governor of Massachusetts Deval Patrick said the men arrested on Wednesday posed no public threat.
"They're not new people to me in the sense that I know the FBI has been asking questions of these folks for several days now," he said.
"Based on the briefings I have had this should not raise concerns in anyone's mind about a continuing threat to the public."
|Fireworks from backpack allegedly belonging to Tsarnaev [Reuters]
Tazhayakov and Kadyrbayev were classmates of Tsarnaev, who attended the University of Massachusetts.
Law-enforcement officials were seen searching dumps in southeastern Massachusetts last week.
The hearing for the three was expected to take place in federal court on Wednesday.
"They are not accused of helping him set up the bombing. They are not accused of helping him at the bombing itself," our correspondent said.
"They are accused of doing things after the bombing that hindered the police inquiry."
Fisher said the details of how the arrests came about were not clear, but the details would be revealed once the charges were laid against the three suspects.
It was thought that the two men from Kazakhstan were already being held on charges related to their visas.
Kadyrbayev's lawyer said his client was being held for violations of his student visa.
The lawyer, Robert Stahl, said his client was "not a target" of the bombing investigation, but declined to comment any further.
He said his client had "cooperated fully" with investigators and "wants to go home to Kazakhstan".
Katherine Shea, a Boston Police spokesperson, said she had no further details to provide on the suspects after their detention was reported on the department's official Twitter feed.