Iranian hackers shut down a British power plant for four days in an unprecedented cyber attack, according to British newspaper The Telegraph.

This is for the first time that Iranian hackers have succeeded in closing down such a facility in the UK, the newspaper reported.

The attack, believed to be the most successful cyber attack of its kind, took place at the same time as a series of attacks on US water infrastructure last month, which affected 12 states and caused concern in the White House.

The Telegraph said British officials did not reveal which power plant had been affected, citing security concerns, but it had learnt that it was a small plant.

Although the outage had no impact on the UK’s wider power supply or energy generation, the UK government briefed the chief executives of power companies and wrote to businesses with advice, direction and next steps.