A special prosecutor who had accused Argentine President Cristina Fernandez de Kirchner of ordering impunity for Iranian suspects in the South American country's worst terrorist attack was found shot dead in his bathroom, authorities said Monday.

Alberto Nisman, who was set to testify Monday in a closed-door hearing, was found in the bathroom of his Buenos Aires apartment late Sunday, federal prosecutor Viviana Fein told Telam, Argentina's official news agency.

'We can confirm that it was a gunshot wound, .22 caliber,' she said, adding that it was too early in the investigation to know what had happened.

Police carry the remains of prosecutor Alberto Nisman outside his house in Buenos Aires, Argentina, early on Monday

Federal prosecutor Viviana Fein confirmed that Mr Nisman died of a .22 caliber gunshot wound. Pictured is an Argentine Federal Police forensic unit carrying his body away from his home

Alberto Nisman (left) was found shot hours before he was due to present a case against Argentine President Cristina Fernandez (right), who he accused of protecting Iranian suspects in a 1994 bombing in Buenos Aires

Nisman had been appointed 10 years ago by Fernandez's late husband, then President Nestor Kirchner, to investigate the 1994 bombing of the Argentine-Israeli Mutual Association in Buenos Aires, which killed 85 people and injured more than 200. In 2013, Argentina and Iran reached an agreement to investigate the attack, which remains unsolved.

That year, Nisman released an indictment accusing Iran and Hezbollah of organizing the blast. Iran denies any involvement.

Last week, Nisman accused Fernandez and other senior Argentine officials of agreeing not to punish at least two former Iranian officials in the case. He asked a judge to call Fernandez and others, including Foreign Minister Hector Timerman, for questioning.

'The president and her foreign minister took the criminal decision to fabricate Iran's innocence to sate Argentina's commercial, political and geopolitical interests,' Nisman said last week.

Government officials called the prosecutor's allegations ludicrous.

A federal judge had begun the process of deciding whether to hear the complaint and whether anyone should be summoned for questioning.

Late Sunday, federal police agents in charge of Nisman's protection alerted their superiors that he wasn't answering phone calls, according to a statement from the Health Ministry. When he also didn't answer the door, they decided to alert family members, according to the statement.

When Nisman's mother wasn't able to open the door because a key was in the lock on the other side, a locksmith was called to open it, the ministry said. A .22 caliber handgun and a shell casing were found next to Nisman's body.

Israel's foreign ministry expressed 'deep sorrow' over Nisman's death.

'Nisman, a courageous, venerable jurist who fought intrepidly for justice, acted with determination to expose the identities of the terrorists and their dispatchers,' a ministry statement said.

Firefighters and rescue workers search through the rubble of the Buenos Aires Jewish Community center in this July 18, 1994, picture, after a car bomb rocked the building, killing 86 people. Mr Nisman believes there has been a cover-up over finding the culprits

Late Sunday, federal police agents in charge of protecting Nisman (pictured) alerted their superiors that he wasn't answering phone calls