Special prosecutor Alberto Nisman was found shot dead in the bathroom of his Buenos Aires apartment late on Sunday, authorities said.

Nisman, 51, was appointed 10 years ago by late Argentinian President Nestor Kirchner to investigate the 1994 bombing of a Jewish community center in the capital that killed 85 people.

Last week, Nisman accused current President Cristina Fernandez, Kirchner's widow, of back channel deals with Iran so as to avoid investigating the attack. A legal suit he filed accused Fernandez of working to absolve the Iranian officials accused of orchestrating the attack.

Nisman was due to testify on Monday in a closed-door hearing with Congress over his claim.

"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. He said the deal was meant to foster trade between the two countries - providing oil to Argentina in exchange for grain exports.

Argentina and Iran agreed in 2013 to establish a "truth commission" that would create a legal report about those implicated in the 1994 attack, and then interview them in Tehran. The deal limited questioning to five suspects named in Interpol alerts, including former Iranian Defense Minister Ahmad Vahidi.

The attack remains unsolved.

Apartment door locked from the inside

Nisman's body was found after his security detail, unable to reach him by phone or at his front door, alerted his family. Nisman's mother called a locksmith after the door was found locked with a key inserted into the deadlock on the inside of the apartment.

"Alberto Nisman was found dead on Sunday night in his flat on the 13th floor of the tower Le Parc, in the Buenos Aires district of Puerto Madero," the Argentine Security Ministry said in a statement.

"Next to Nisman's body ... a 22-calibre handgun was found, together with a bullet casing."

An autopsy will be carried out in the coming days.

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

jr/bw (Reuters, AP, dpa)