Elexon, a company that plays a central role in the balancing and settlement of the UK power system, said Thursday it has suffered a cyber attack that affected its internal networks, cutting off email access for its employees.

“We are advising you that today that Elexon’s internal IT systems have been impacted by a cyber attack. BSC Central Systems and EMR are currently unaffected and working as normal. The attack is to our internal IT systems and Elexon’s laptops only,” the company said in a short statement on its website.

In a subsequent tweet posted later in the day the company added that it had identified the root cause of a cyber attack and was working to resolve the issue. However, Elexon did not disclose the nature of the cyber attack.

“BSC Systems (and their data) and EMR are currently unaffected and working as normal,” Elexon said.

The UK's National Grid ESO, Britain’s national electricity system operator, said it is aware of the cyber attack against Elexon and that the incident did not affect electricity supply across the UK.