An Argentine prosecutor who accused president Cristina Kirchner of obstructing a probe into the 1994 Jewish centre bombing has been found shot dead, just hours before he was due to testify at a congressional hearing.

Alberto Nisman, 51, was found overnight in his apartment in the trendy Puerto Madero neighbourhood of the capital Buenos Aires.

Since 2004, he had been investigating the 1994 van bombing of the building of the Argentine Jewish Charities Federation, or AMIA.

Eighty-five people were killed and 300 others injured in Argentina’s worst attack of its kind.

“I can confirm that a .22-caliber handgun was found beside the body,” prosecutor Viviana Fein said.

“Death is due to gunshot.”

Authorities said Mr Nisman had been found by his mother in the bathroom of his 13th-floor apartment after his security detail was unable to contact him.

Last week, Mr Nisman asked for an investigation into possible obstruction by president Kirchner and was due to speak at a congressional hearing on Monday to provide evidence of his assertions.

Opposition lawmaker Patricia Bullrich said she was shocked by Mr Nisman’s death, calling it “a grave affront to the country’s institutions”.

She said she had spoken to him on the phone on Saturday on three occasions and he said that he had received several threats.

Ms Bullrich added that parliament would meet to discuss the killing.

Grain-for-oil deal saw Argentina protect suspects: prosecutor

Mr Nisman accused Iran of being behind the bombing and said Ms Kirchner had hampered the enquiry to curry favour with the Islamic republic.

He said the president had opened a secret back channel to a group of Iranians suspected of planting the bomb.

Mr Nisman said the scheme intended to clear the suspects, so Argentina could start swapping grains for much-needed oil from Iran, which denies any connection with the bombing.

The Argentine government also categorically denied the accusations.

Since 2006, Argentine courts have demanded the extradition of eight Iranians, including former president Akbar Hashemi Rafsanjani, former defence minister Ahmad Vahidi and Mohsen Rabbani, Iran’s former cultural attaché in Buenos Aires.

Argentina charges that Hezbollah, the Lebanese Shiite movement, carried out the attack under orders from Iran, which Tehran denies.

Mr Nisman said he had phone recordings that showed the Kirchner government and Argentine authorities had bowed to Iranian demands, after the Islamic republic dangled lucrative commercial contracts.

He was supposed to present proof of his allegations that Ms Kirchner and foreign minister Hector Timerman had a “plan of impunity” to “protect the Iranian fugitives”.

Jewish community members had cautiously welcomed Mr Nisman’s complaint, but also requested he make public the evidence to back up his assertions.

The Jewish centre bombing came two years after an attack on the Israeli embassy in Buenos Aires which killed 29 people.

In January 2014, Argentina accused Israel of concealing information about the attacks, after a former Israeli ambassador to Argentina suggested that those responsible had been killed by Israeli security forces.

Argentina’s Jewish population of about 300,000 people is the largest in Latin America.

Cristina Kirchner

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