Spain’s high-voltage electricity grid suffered more power generation disruptions than previously known ahead of the country’s largest ever blackout, the government said.

Spain suffered several power glitches and industry officials sounded repeated warnings about the instability of its power grid in the build up to its catastrophic blackout on Monday. The government has ordered several investigations into the blackout.

Red Eléctrica, Spain’s electricity grid operator, ruled out a cyberattack, human error or unusual weather. Experts say it could take weeks to determine the cause.