An investigation has been opened into the death in custody of a young Iranian in Tehran's infamous Evin prison, the judiciary said Tuesday, with a lawmaker linking the death to recent protests.

"An investigation was immediately opened and the prison guards and other people have been interrogated," said Tehran's chief prosecutor Abbas Jafari Dolatabadi, according to the judiciary-linked Mizanonline.

A reformist lawmaker, Mahmoud Sadeghi, had earlier tweeted: "Unfortunately, one of the protesters arrested in the recent troubles is dead in Evin prison."

Other officials denied the claim, saying the individual, identified as Sina Ghanbari, was linked to drug-trafficking and had committed suicide.

"This individual was not arrested during the recent protests and had nothing to do with the recent demonstrations," an unnamed judicial official told the reformist ILNA news agency.

Another prison official said Ghanbari had hanged himself in the toilets.

The outspoken MP, Sadeghi, had earlier warned of a "second Kahrizak" after the protests that rocked the country for five days over the new year.

Kahrizak was a notorious prison in south Tehran where at least three protesters were tortured to death during mass demonstrations in 2009.

The prison was shut down and several officials put on trial, with the city's chief prosecutor at the time, Said Mortazavi, sentenced to two years in prison in November for his role in one of the deaths.

Various figures have come from official sources over the number arrested over the recent unrest which hit several dozen towns and cities, with Sadeghi putting the total at 3,700.

Officials have said the majority have since been released, with only the main "instigators" facing trial.