Power supply was cut across Turkey on Tuesday, halting public transit systems and resulting in major traffic jams in cities, including Ankara, Istanbul and Izmir.
The Turkish Electricity Distribution Company blamed a fault on power transmission lines for the outage, but Prime Minister Ahmet Davutoglu said authorities were "considering all probabilities behind the nationwide power outage, including terrorism", Xinhua news agency reported.
Metro and train services were halted in major cities, and ground traffic was blocked as all signal systems were disturbed.
Services at hospitals, including surgeries, were been affected.
The energy ministry set up a crisis centre in Ankara. Energy and Natural Resources Minister Taner Yildiz said this is the worst power cut in 15 years in the country.
Efforts were being made to restore power supply in the country.