A Bahraini suspect held for questioning in connection with a bomb attack that killed a woman in late June has died in prison, a local newspaper reported on Sunday, while another news website has suggested he may have died under torture.

The interior ministry said in a statement that a detainee held on unspecified charges died at a hospital on Saturday evening of ‘natural causes’.

The statement did not name the detainee, but the Arabic-language al-Wassat newspaper identified him as 35-year-old Hassan Jassem Hassan al-Hayki and said he was being held in connection with the bombing in the village of al-Aker.

‘The detainee, who was held protectively, was suffering from a health problem,’ the statement said, without giving any details.

Another news website which often reflects the views of Shia opposition groups quoted the family as saying that he had complained of severe torture to force him to confess to charges of links to the bombing.

Authorities did not immediately respond to a request for comment, but Bahrain denies using torture and says it has installed cameras at interrogation centres to guard against abuse.

The interior ministry said earlier this month that it had arrested two men suspected of planting the bomb on June 30 that killed the woman while she was travelling through the village. Her three children were wounded.

The ministry said a third suspect in the blast had fled to Iran from Bahrain.

A Bahraini human rights group challenged the official version of events, citing ‘conflicting narratives’.

Opposition activists have said on social media that witnesses reported seeing security forces fire on the woman's car after it accidentally neared a royal convoy.

The kingdom has accused Iran of fomenting protests by the Shias - a charge denied by Tehran.

 It drew UN criticism in June when it acted to strip a top Shia cleric of his citizenship and closed down the main Shia political opposition group.