South Africa’s former president Jacob Zuma has told a judicial inquiry into corruption allegations that he is the victim of a plot by foreign intelligence agencies to seek his downfall.

Speaking on the first day of five days of testimony, Zuma denied he had presided over an immense system of corruption and patronage that drained billions from the country’s exchequer.

Zuma was ousted last year after almost a decade in power, following a bitter internal battle within the ruling African National Congress party. He faces hours of questioning by Raymond Zondo, a senior judge, mandated to investigate allegations of “state capture” in South Africa during his presidency.

In hearings on Monday morning, Zuma claimed two foreign intelligence agencies had recruited spies within the ANC as part of a scheme to control South Africa and that the inquiry was designed to smear him.

“I have been vilified, alleged to be the king of corrupt people,” he said. “There are people who infiltrated, there are spies who were at work. I asked people in [my] organisation: ‘What have I done?’ They can’t tell me. This commission … must be the grave of Zuma. He must be buried here.”

The inquiry was set up after an ombudsman’s report uncovered apparent evidence of improper contact between three wealthy businessmen brothers – Atul, Ajay and Rajesh Gupta – and senior officials in Zuma’s administration.

The report, which stopped short of asserting criminal behaviour, called for an investigation into whether Zuma, some of his cabinet members and some state companies had acted improperly.

Among the cases it reviewed was an allegation by the then deputy finance minister that the Guptas had offered to secure him his boss’s job, as well as claims that Zuma had directed state firms to award tenders to companies owned by the family.

Zuma has said the three Gupta brothers are his friends but he denies any influence-peddling in their relationship.

The Gupta family denied the accusations and left South Africa around the time that Zuma was ousted.

The inquiry has also heard a series of further serious allegations from witnesses in recent months, describing massive bribes paid to officials by businesses seeking favours.

Throughout the day, the 77-year-old Zuma and his lawyers continued to portray the him as a victim. “I have been provoked and provoked to the last degree … My own family suffers … people forget that I have a family who do not want to hear lies about me,” he said.

Zuma said he could trace the conspiracy against him to the early 1990s, when he received an intelligence report that two foreign intelligence agencies “from big countries” and a branch of the apartheid government had come up with a strategy to get rid of him.

“They took a decision that Zuma must be removed from the decision-making structures of the ANC. That’s why the character assassination, that is the beginning of the process that has put me where I am today,” Zuma said

After the hearing, he addressed hundreds of supporters who had gathered outside the offices of the inquiry in Johannesburg.

Some wore military fatigues emblazoned with the emblem of the former armed wing of the ANC shouted: “Hands off Zuma!”

Natasha Mazzone, a senior parliamentarian with the opposition Democratic Alliance party, said Zuma was trying to whitewash serious allegations: “The fact that we’ve heard a conspiracy theory dating back to 1990 is proof that the real truth is going to take a long time to extract.”

There have been fears that Zuma will use the hearings as a platform to attack his successor, Cyril Ramaphosa, who led the ANC to a convincing election victory in May but has so far been unable to fully assert his authority over the party.

Observers say Ramaphosa needs to move quickly to root out entrenched networks of patronage and graft, often involving individuals who owe senior positions within the party or public administration to Zuma.

Zuma faces a separate corruption investigation involving 16 charges of fraud, racketeering and money laundering relating to a deal to buy European military hardware to upgrade South Africa’s armed forces in 1994. He denies the charges.