The elderly father of the second in command of Bahrain's largest Shiite opposition group Al-Wefaq died of his injuries on Thursday after riot police attacked him a day earlier, the organisation said.
"Ali Hasan al-Dehi, 70, was attacked by riot police forces Wednesday evening" and died early Thursday, Al-Wefaq's website reported.
His son, Hussein al-Dehi, is deputy head of Al-Wefaq.
The statement said the elder Dehi had told one of his sons, who had arrived home to find him on the floor, that "he had been beaten by riot police."
Al-Wefaq member and former MP Sayed Hadi Moussaoui told AFP police were dispersing a protest in the western village of Dehi, when the man was attacked.
Moussaoui said members of the Dehi household were harassed several times by the authorities, adding that the dead man's wife had been "insulted" in the past without giving further details.
Later on Thursday, the ministry of health issued a statement saying that Dehi had "died of natural causes."
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The statement, carried by state news agency BNA, said that the man had fainted on Wednesday at home and was then taken to Salmaniya Medical Complex, where, according to his medical file he was suffering from cardiac problems.
He died of "a heart attack and hypertension," said the statement.
Earlier this year, Bahrain's Sunni monarchy crushed pro-democracy protests, spearheaded by the majority Shiites, with the help of troops from other Gulf states, such as Saudi Arabia.
Twenty-four people died during the crackdown, between mid-February and mid-March, according to official figures from Manama.
Four protesters have since died in custody.
The Gulf kingdom is awaiting a report by an independent commission of inquiry into the crackdown, which is expected on November 23.
Though mass protests have ended, tensions remain high as the trials of dozens of opposition figures and protesters continue in the capital.