The US is tightening its screening of international students, its first security change in response to the Boston Marathon bombings last month.

The move comes after a student from Kazakhstan - who did not have a valid visa - was accused by police of hiding evidence for one of the bomb suspects.

The Department of Homeland Security has ordered border agents to automatically check the visa status of every student.

Azamat Tazhayakov had returned to the US despite being dismissed from school.

The 19-year-old appeared in court on Wednesday, accused of helping to throw out a backpack belonging to his friend, Boston bombing suspect Dzhokhar Tsarnaev.

Tazhayakov's student visa had been terminated by the time he arrived in New York on 20 January, following his academic dismissal from the University of Massachusetts-Dartmouth on 4 January.

The Department of Homeland Security will "effective immediately" verify that every international student visa is valid, according to an internal memo obtained by the Associated Press news agency on Friday.

Under the new procedures, border agents will verify a student's visa status before the person arrives in the US, using information provided in flight manifests.

If that information is unavailable, they will manually check the visa status through a US database.

Beforehand, border agents would only verify a student's status in a database, the Student and Exchange Visitor Information System, when the person was referred to a second officer for additional inspection or questioning.

Tazhayakov was not sent to a second officer when he arrived, because there was no information to indicate he was a national security threat, said Peter Boogaard, a spokesman for the Department of Homeland Security.

Tazhayakov is not implicated in the planning of the attacks, but he and fellow 19-year-old Kazakh, Dias Kadyrbayev, face up to five years in prison if convicted of obstructing the FBI investigation.

According to police, Tazhayakov and Kadyrbayev removed items from Dzhokhar Tsarnaev's dormitory room at the University of Massachusetts - Dartmouth, three days after the blasts, including a backpack filled with fireworks remains.

Tsarnaev, 19, sustained gunshot wounds during the police manhunt days after the bombings, and remains in a prison hospital. He faces a possible death sentence if convicted.

Three people died and more than 260 were wounded after two explosive devices made from pressure cookers detonated near the Boston Marathon finish line on 15 April.

On Friday, a Massachusetts funeral director said the main suspect's older brother, Tamerlan Tsarnaev, had died from gunshot wounds and blunt trauma to his head and torso.

The 26-year-old was killed several days after the bombing following a shootout with police, when he was run over by his younger brother as he fled the scene in a vehicle, authorities have already said.

His body was initially taken to another funeral home, where it was greeted by about 20 protesters on Thursday night.