An Indian court sentenced 38 people to death on Friday over a string of bomb blasts in 2008 that killed dozens in the western city of Ahmedabad.

The court had on February 8 convicted 49 people over the coordinated attacks that killed 56, launching shrapnel through markets, buses and other public places in Gujarat state's commercial hub.

"Special judge A R Patel awarded death sentence to 38 out of the 49 convicted," said special public prosecutor Amit Patel.

"Eleven of the convicted were sentenced to life imprisonment till death."

A group calling itself the Indian Mujahideen claimed responsibility, and said the act was revenge for 2002 religious riots in the state that left some 1,000 people dead.

Nearly 80 people were charged for the 2008 Ahmedabad attacks but 28 were acquitted, according to prosecutor Amit Patel.

The convicted were all found guilty of murder and criminal conspiracy, he added.

The marathon trial lasted nearly a decade -- thanks to India's labyrinthine legal system -- with more than 1,100 witnesses called to testify.

It was dragged out by procedural delays, including a legal battle by four of the accused to retract confessions.

Police also foiled a 2013 attempt by more than a dozen of the defendants to tunnel their way out of jail using food plates as digging tools.

All 77 accused have been held in custody for years, with the exception of one who was bailed after a schizophrenia diagnosis.

Ahmedabad was the centre of deadly 2002 religious riots that saw at least 1,000 people -- mostly Muslims -- hacked, shot and burned to death.

The violence was prompted by the death of 59 Hindus in a train fire -- a case in which 31 Muslims were convicted for criminal conspiracy and murder.

Prime Minister Narendra Modi was then head of the state government and has subsequently been dogged by accusations of turning a blind eye to the violence.

India was rocked by several lethal bomb attacks in 2008 claimed by the Indian Mujahideen group -- with dozens killed in the capital New Delhi and northern tourist city of Jaipur. 

In November of that year, 166 people were killed by gunmen armed with explosive devices, in a coordinated assault on hotels and other high-profile targets in Mumbai that was blamed on Pakistan-based militants.