Argentina's president has called for an overhaul of the country's intelligence services, using her first public comments since the mysterious death of a prosecutor to reject accusations against her.

Without saying who might have killed Alberto Nisman, Cristina Fernandez called on congress to dissolve Argentina's spy agencies.

In recent letters, she had suggested rogue intelligence agents may have orchestrated the death of the prosecutor hours before he was to give potentially explosive evidence to politicians on the alleged cover-up.

But she provided no new details of the alleged plot during her nationally televised speech, and she herself oversees the intelligence agencies in question.

While government officials had labelled Mr Nisman's allegations as absurd, the speech was the first time President Fernandez had taken them on directly.

"It's unreasonable to think our government could even be suspected of such a manoeuvre," said Ms Fernandez, speaking in a wheelchair after she fractured an ankle.

Mr Nisman, 51, was found dead on January 18 in the bathroom in his apartment, a bullet in his right temple, a .22 calibre gun next to him.

His death came days after he gave a judge a report alleging Ms Fernandez secretly reached a deal to prevent prosecution of former Iranian officials accused of involvement in the 1994 bombing of Argentina's largest Jewish centre. The attack killed 85 people and injured more than 200.

She allegedly reached the deal in exchange for economic and trade benefits with Iran.

Mr Nisman's death sparked anti-government protests and a myriad of conspiracy theories, ranging from suicide to the involvement of Iranian intelligence agents.

Appearing rested and calm, Ms Fernandez began with a spirited defence of all her government had done to try to solve the 1994 bombing of the centre.

She lamented that more than 20 years later nobody had been convicted or even detained. She noted that her predecessor, husband and former president Nestor Kirchner, had appointed Mr Nisman to the case after years of paralysis.

She said a 2013 memorandum of understanding with Iran, which many in the country have bitterly criticised, was aimed at obtaining co-operation with the Middle Eastern powerhouse to finally seek justice for the bombing. Iran has repeatedly denied any involvement.

Ms Fernandez, 61, said a reform of the intelligence services would be presented to congress by the end of this week. She said the structure of a new "federal intelligence agency" would have a director and deputy and only a few in government would have access to the agency heads - apparently a critique of a system where many in Congress have contact with intelligence officials.

She said that reforming the clandestine services was a "national debt" the South American country has had since the return of democracy in 1983. Argentina had several years of a brutal dictatorship and Ms Fernandez suggested that the problems of today had their roots in the years of that military government.

In her two letters the last week, she suggested Mr Nisman's death was a plot against her government possibly orchestrated by intelligence services, which had fed false information to Mr Nisman.

In her first letter, published on January 19, she suggested that Mr Nisman committed suicide. Three days later, however, she did an about-face, suggesting that he had been killed. She was roundly criticised by many in the country for communicating via social media instead of in public.

Employing the fiery rhetoric she is known for, at the end of her televised speech she looked directly into the camera and said in a stern tone that she had a message for her countrymen.

"I will not be extorted, I am not afraid" of being cited by judges or denounced by investigators, she said. "They will not make me move even a centimetre from what I have always thought."

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