Eskom must launch an investigation into allegations the African National Congress (ANC) is involved in corruption at the power utility before it can respond to a demand for an apology and retraction of comments by former Eskom CEO André de Ruyter.

In a bombshell interview with e.tv's Annika Larsen, De Ruyter said he believed, according to evidence he had seen, the power utility had become a feeding trough for the ANC.

This prompted a barrage of unfounded attacks on De Ruyter by senior ANC officials and a letter of demand through the party's attorney, Krish Naidoo.

In a letter addressed to Eskom board chairperson Mpho Makwana on February 28, the ANC demanded a retraction of the comments as well as clarity on whether De Ruyter had spoken for Eskom.

After granting a seven-day extension, Naidoo confirmed to News24 Eskom responded on Tuesday - requesting even more time.

"The interview by Mr De Ruyter contained a number of serious allegations. You will appreciate that the responsible course of action for Eskom is to evaluate these allegations and to establish all the relevant facts," a letter written by Eskom's group executive for legal and compliance, Mel Govender, read.

"Eskom must consider what actions it must take having regard to the determination of the facts. This may take some time and accordingly Eskom cannot commit to giving you the response you have sought from Eskom," Govender said.

She stated as soon as Eskom was in a position to speak about the allegations, it would inform the ANC.

Govender also confirmed letters for De Ruyter's attention had been delivered to his last known address - but Eskom had not yet received a response.

Naidoo, on behalf of the ANC, responded within two hours, saying it was understandable Eskom would require time to investigate De Ruyter's allegations.

"However, the ANC's request is for a decision on one issue only … whether the public utility confirms or disassociates itself from the defamatory utterance of Mr De Ruyter pertaining to the ANC," he wrote in an email to Govender that he shared with News24.

He said Makwana had said De Ruyter's interview and comments were "reprehensible" and suggested the Eskom board could meet virtually to take a decision on this narrow matter, to avoid incurring expenses of a physical meeting.

"Beyond the seven-day indulgence given to Eskom in our last correspondence, the ANC is not prepared to grant any further indulgence. If the ANC is dilatory about commencing litigation, you will appreciate that, with the passage of time, its resolve and integrity could be placed in issue," Naidoo said.

He also raised concerns about the lack of response from De Ruyter on the letter Eskom helped the ANC deliver.

"Kindly advise if Eskom has been able to establish whether Mr De Ruyter still occupies the premises?" he asked.

De Ruyter has gone to ground in the aftermath of the interview and has not spoken publicly since he was asked by the Eskom board to leave the utility immediately in the days after the interview was aired.