An Indian court sentenced two convicts to death Thursday in connection with the country's deadliest bombings, a series of blasts that rocked Mumbai two decades ago and claimed more than 250 lives.

Firoz Abdul Rashid Khan and Taher Merchand were convicted of conspiracy and murder in the 1993 blasts and handed the death penalty in the case's final sentencing on Thursday.

"It was a historic judgement and its impact will reverberate for years," public prosecutor Ujjwal Nikam told AFP.

A key figure in the attacks, Abu Salem, was sentenced to life imprisonment, along with Karimullah Khan, for their roles in the 12 bomb blasts that killed 257 people and injured hundreds more.

India had to agree that Salem would not receive the death penalty when he was extradited from Portugal.

A fifth man, Riyaz Siddiqui, was sentenced to 10 years in prison, Nikam said.

The sentences come after a special court in Mumbai convicted the men in June on a range of offences in the attacks. Another accused, Mustafa Dossa, died of a heart attack shortly after the convictions.

The court had acquitted a seventh man, Abdul Quayyum, for lack of evidence.

The men were found guilty of involvement in coordinated bomb attacks on the Mumbai stock exchange, the headquarters of Air India and a shopping centre in March 1993.

The attacks were believed to have been staged by Mumbai's Muslim-dominated underworld in retaliation for anti-Muslim violence that had killed more than 1,000 people a few months earlier.

Salem went on the run after the 1993 attacks and was only extradited from Portugal in 2005.

Salem is a former associate of Dawood Ibrahim, India's most wanted criminal, who allegedly masterminded the 1993 blasts.

Thursday's hearing concluded the long-running case that at its outset involved 189 defendants.

The culprits sentenced Thursday were detained and tried separately from other suspects in the case as they were arrested towards the end of a previous trial, in which 11 people were sentenced to hang for perpetrating the deadly blasts.

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Ten of those earlier sentences were later commuted to life in prison while one, Yakub Memon, was executed in 2015 -- a decade after he was convicted under controversial anti-terror legislation that is no longer on the statute books.

"Some defendants have absconded from India and others are serving their sentences in jail. Only three convicts have received death penalty so far," Nikam said.

The attack also embroiled Bollywood star Sanjay Dutt, who served time for buying weapons from gangsters accused of orchestrating the bombings before walking free last year.