April 24 (Reuters) - Spain's antitrust and energy watchdog CNMC has added more power companies, including local units of France's TotalEnergies TTEF.PA and Engie ENGIE.PA, to the list of firms being investigated over last year's unprecedented blackout in Spain and Portugal, it said on Friday.

Last week the CNMC opened formal probes after finding evidence that some power sector rules were breached over extended periods, possibly contributing to the crippling outage on April 28, 2025.

It then said it was investigating Spanish grid operator Red Electrica (REE) - a unit of Redeia REDE.MC - and energy companies Iberdrola IBEMC>, Naturgy NTGY.MC, Endesa ELE.MC, and Repsol REP.MC, as well as individual power plants.

Now it has also opened sanctions procedures against Engie Cartagena and TotalEnergies Clientes, among others. Engie and Total did not immediately reply to a request for comment.

CNMC head Cani Fernandez had previously said the most serious breaches could lead to a fine of up to 60 million euros.

The sanction procedures have a maximum duration that varies between nine and 18 months, depending on the severity of the infraction, it said.