Boston bombing suspect Dzhokhar Tsarnaev has pleaded not guilty on all charges in connection with the April attacks, some of which could carry the death penalty.

In his first court appearance on Wednesday, the 19-year-old entered the federal courtroom in Boston in handcuffs, shackles and wearing an orange jumpsuit.

"Not guilty," said the US citizen, whose family hail from Chechnya. He repeated his plea repeatedly as the 30 counts were read out at the arraignment, which lasted seven minutes.

Tsarnaev was arrested five days after the bombing of the Boston Marathon on Monday, April 15. His brother, Tamerlan, was shot dead by police during a city-wide manhunt following the blasts.

The courtroom was packed with victims of the bombings, some of whom needed canes to walk.

Also in court were many journalists and a few people who identified themselves as friends of Tsarnaev.

He is accused of using a pressure cooker bomb - termed a "weapon of mass destruction" by US law - in the attack, which left three people dead and more than 260 wounded.

He is also charged in connection with the shooting death of a campus police officer at the Massachusetts Institute of Technology during the brothers' wild overnight getaway attempt.

Seventeen of the counts against him are punishable by the death penalty or life imprisonment.

The attacks stunned America with scenes of carnage and chaos at one of the country's premier sporting events.

The bombs were packed with metal fragments to cause maximum damage, injuring about 264 people, with many losing their legs.