US police arrest three suspects in Boston bombing

US police announced on Wednesday that they had arrested three more suspects as part of their investigation into a bomb attack on the Boston marathon that left three dead and more than 260 wounded.

"Three additional suspects taken into custody in Marathon bombing case. Details to follow," the Boston Police Department said on Twitter.

One of two ethnic Chechens, 19-year-old Dzhokhar Tsarnaev, was already in custody and has been charged with carrying out the bombing.

His brother, 26-year-old Tamerlan Tsarnaev, was killed on April 18 during the manhunt for the pair.

The brothers are alleged to have detonated backpacks holding pressure cookers packed with explosives near the finish line of the April 15 race. They are also accused of killing a police officer during their time on the run.

Boston police did not immediately offer more details of the arrests, but the Boston Globe newspaper reported the new suspects were college students who are alleged to have helped Dzhokhar after the attack.

Officials have said they are investigating a recent period Tamerlan spent in the volatile North Caucasus region of Russia and intelligence reports that he had developed an increasingly radical view of his Islamic faith.

But investigators have not suggested the pair were part of a larger group.