A London-based NGO, the Bahrain Institute for Rights and Democracy (BIRD), had earlier called for an investigation into the death of 32-year-old Mohamed Almosawi, who was arrested at a checkpoint on March 19.

It said his family had been contacted on Friday morning to collect his body from a military hospital in the Gulf kingdom.

BIRD had published photos showing bruises and injuries on his face, body and feet, "raising serious concerns that he was subjected to torture prior to his death".

Almosawi was held "in connection with a case of espionage, communication, and transmission of information" to Iran's Revolutionary Guards about the country's strategic sites "with the aim of targeting them", the interior ministry said.

"The Public Prosecution's special investigation unit has been tasked with investigating the incident and verifying the circumstances of the injuries as well as the causes that led to the death," it added.

The ministry claimed that photos circulating on social media were "inaccurate".

Bahrain is ruled by a Sunni Muslim dynasty, but the tiny kingdom has a large Shia population that has long complained of marginalisation.

Human Rights Watch (HRW) last week expressed alarm after the arrests of "dozens of people" since the US-Israeli offensive against Iran began on February 28.

Some of those detained were accused of treason, while others were arrested for protesting.

The arrests also come at a time when Gulf countries are concerned about Iranian infiltration as they come under attack, with Qatar, Kuwait and the UAE all cracking down on what they call Iran-related networks.

Videos posted by activists from Almosawi's funeral later Friday in Muharraq in north Bahrain showed a large crowd of angry men following his coffin.

Almosawi had previously spent 12 years in prison, like hundreds of protesters jailed during pro-democracy demonstrations inspired by the Arab Spring in 2011.

He was among around 1,500 prisoners pardoned and released in 2024.