An Indian fisherman died after being electrocuted in a jail in the Pakistani port city of Karachi on Monday, prompting a leading human rights activist to demand an inquiry into the "mysterious circumstances" of his death.

Bhagwan Das Majithia, 25, was electrocuted when he touched a pipe in a bathroom on Monday morning, Landhi Jail Superintendent Nusrat Sanghan said.

Majithia, hailing from Gujarat, was arrested along with 16 other fishermen on April 24 for illegally fishing in Pakistani waters.

He was the second Indian prisoner to die while being held in Landhi Jail within four months.

Laxman Kanji, a 40-year-old fisherman, died of cardiac arrest after being rushed to hospital from the prison on March 20.

Earlier reports had said Majithia died of an electric shock he suffered while switching on a washing machine.

Majithia had gone along with other prisoners to a section of the jail to wash clothes on Monday morning when the incident occurred, TV news channels reported.

Former human rights minister Ansar Burney said he had asked authorities to conduct a probe as Majithia had died in "mysterious circumstances".

"This man was a prisoner and it is a bit hard to believe that a prisoner can die of an electric shock. It is not as if he was at home or at his workplace and could have been exposed to electrical equipment that could have caused his death," Burney told PTI.

"I have asked authorities to ensure that Majithia's death is investigated to find out what exactly happened," he said.

Officials of the Indian high commission said they had not yet been formally informed about the fisherman's death.

They said a committee set up by India and Pakistan to study the problems of prisoners had recommended that authorities should be immediately informed about deaths of prisoners in jail.

The officials said consular access had been granted to Majithia in April and his status as an Indian national had been confirmed at that time.

Majithia was a resident of Junagadh district of Gujrat. The authorities of Landhi Jail informed the government of Sindh province about Majithia's death.

The provincial government later informed the federal government. Scores of Indian fishermen arrested for illegal fishing are being held in Landhi Jail.

India and Pakistan frequently detain each other's fishermen for violating maritime boundaries. Pakistan last month freed 99 Indian prisoners, including 96 fishermen, as a goodwill gesture during a visit to Islamabad by External Affairs Minister Pranab Mukharjee.

Four Pakistani nationals have died in Indian jails in the past few months. Indian authorities said they had died of natural causes, but their relatives allege that they were ill-treated in prison.

The two countries recently formed a joint committee of retired judges to ensure the humane treatment of prisoners and to recommend measures to expedite their release. The Indian members of the panel visited Pakistani jails this month and met Indian prisoners in Karachi, Lahore [Images] and Rawalpindi.