Rahman, 50, has been tried in absentia after he fled the country for London in 2008.

He now leads the main opposition Bangladesh Nationalist Party (BNP) from exile after Zia was jailed in February for five years for corruption.

“We thank God for the verdict,” prosecutor Mosharraf Hossain told reporters on Wednesday amid tight security.

“We hoped that Tarique Rahman would get the death sentence,” he said, adding the court observed that Rahman played a key role in the attack.

Hasina was addressing the rally when the grenades exploded and suffered severe injuries in one ear. Among the dead was the wife of a former president.

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Four years later, Hasina stormed back to power after leading a secular coalition to a landslide victory in elections in December 2008.

Two other ministers, former heads of the intelligence agencies and police and a key aide of Zia were also facing death sentences in the case.

Three Islamist extremists were also charged over the attack and later executed in a separate trial. Death sentences are common in Bangladesh, with hundreds of people on death row. All executions are by hanging, a legacy of the British colonial era.

At least nine top Islamist extremists, five leaders of the country’s largest Islamist party and a senior opposition leader have been hanged in Bangladesh’s jails since 2007.

Rahman’s lawyer Sanaullah Mia said the charges against his client were politically motivated.

He questioned the timing of the verdict, saying it was aimed at keeping Rahman out of elections expected for December.

“There was no evidence or witness against him. No witness could say that conspiracy was hatched at Hawa Bhaban,” he said, referring to a former BNP office used by Rahman.

Police spokesman Sohel Rana said security was tightened in courts and across the South Asian nation to avert any violence following the verdict.

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“Police are fully prepared to prevent any violence centring on the verdict,” he said earlier.

Zia was transferred to hospital last weekend from the 19th-century Dhaka Central Jail, where she is the only prisoner.

She has been on trial in a special room of the prison on additional corruption charges that her supporters say are politically motivated.

The 73-year-old was already suffering from health issues including arthritis, diabetes and knee replacements when she was sentenced in February.

Her party boycotted the 2014 election in which Hasina returned to power but is expected to contest the election due in December.