Beleaguered South African power utility Eskom appointed an interim CEO on Friday, capping a week of high drama marked by a bombshell interview in which the firm's previous head accused the ruling party of graft.

The company said its chief financial officer, Calib Cassim, would take the helm "with immediate effect" following the sudden departure of his predecessor, Andre de Ruyter.

"Mr Cassim will lead the Eskom management team until further notice," the company said in a statement.

South Africa is in the midst of a severe energy crisis, with record power cuts that have hampered economic growth and angered the population.

The appointment of Cassim, a registered accountant with a 20-year career at the state-owned firm, comes two days after de Ruyter was asked to leave hours after giving an incendiary interview to a local broadcaster.

Speaking to eNCA television, De Ruyter expressed doubts about the political will to end endemic graft at the power utility.

Asked if the firm, which provides about 90 percent of South Africa's electricity, was a "feeding trough" for the governing African National Congress (ANC), he said "evidence suggests that it is."

A "high-level" politician was involved in the wrongdoing, De Ruyter added, suggesting a cabinet minister was aware of the fact.

The ANC has refuted the claims, with party secretary-general Fikile Mbalula on Thursday accusing De Ruyter of "incompetence" and having failed at his job.

Mbalula told a press briefing the party was considering taking legal action against the former CEO, who he suggested held nurtured ambitions.

- 'Cyanide coffee' -

De Ruyter, who took over as CEO in 2020, resigned in December but was due to vacate his office at the end of March to give Eskom time to find a successor.

In the interview he said crime groups were stealing around one billion rand ($55 million) a month from the debt-laden company.

De Ruyter also said he suffered a poisoning attempt in December, around the time of his resignation, drinking coffee laced with cyanide, which left him "shaking badly" and "gasping for air".

A police investigation is underway.

De Ruyter compared corruption at the firm to a cancer which "has just metastasised and has now grown throughout the entire body of the organisation."

Defend Our Democracy, anti-graft campaign group, said on Friday it was "troubling" that instead of dealing with the substance of De Ruyter's claims, some politicians had attacked him.

Scheduled blackouts have burdened Africa's most industrialised economy for years, with Eskom failing to keep pace with demand and maintain its ageing coal power infrastructure.

But the power cuts have reached new extremes, with the country experiencing a record 207 days of power outages last year alone, compared to 75 days in 2021.

Outages cost hundreds of millions of dollars in lost output each day, according to opposition estimates.

De Ruyter had come under pressure from some government ministers who accused the company of not properly attending to the crisis, which analysts say is the result of years of mismanagement, disrepair and corruption.

John Steenhuisen, the head of the leading opposition party, the Democratic Alliance (DA) said the former CEO was "a national hero."

"I applaud and thank him for showing the bravery we all need to fix South Africa," Steenhuisen wrote on Twitter.

Earlier this month, President Cyril Ramaphosa announced a national state of disaster and the appointment of an electricity minister in a bid to intensify the response to the energy crisis.