JOHANNESBURG (Reuters) – South African police said on Thursday they had arrested a number of people, including two former senior managers of Eskom, on suspicion of involvement in fraud and corruption worth 745 million rand ($51 million) at the troubled state-run power firm.

The managers, as well as two business directors and seven companies, are expected to appear in court on Thursday to face the police allegations, which also included money laundering, South Africa’s elite police unit the Hawks and National Prosecuting Authority said in a joint statement.

The individuals, who were not named, were arrested earlier in the day following an investigation into the construction of large projects at two power stations, the statement said.

This revealed “gross manipulation” of contracts between contractors, Eskom employees and third parties at one of them, it continued.

“Eskom continues to work with law enforcement agencies … to root out corruption and malfeasance,” the power provider said in a statement, adding the names of the individuals could not be revealed until they appeared in court.

“We … will leave no stone unturned in ensuring that perpetrators … are brought to book,” it added.

The ailing utility, which provides 90% of South Africa’s power, has been struggling to keep the lights on amid serious financial problems in part stemming from years of mismanagement and alleged graft.

Last week, it had to implement some of the most far reaching planned blackouts in years and is regularly cited by ratings agencies as one of the main risks to South Africa’s economy.

“This is a great milestone in the fight against corruption in our country,” South Africa’s Special Investigating Unit, which was also looking into the allegations, said.

Eskom’s problems are a headache for President Cyril Ramaphosa, who has staked his reputation on fixing ailing state-owned firms and reviving South Africa’s flagging economy.

($1 = 14.7075 rand)

Reporting by Emma Rumney and Mfuneko Toyana; Editing by Tim Cocks and Mark Potter