( CNN ) A massive power outage spread across Turkey on Tuesday , blacking out a broad swath of the country and affecting some flights . Prime Minister Ahmet Davutoglu said all possible causes were under investigation , including terrorism . Trams and subways were idled in Istanbul -- with more than 14 million inhabitants , the largest city in the country and the fifth largest in the world . Homes and offices were left without electricity . `` I am sitting in my apartment , '' CNN producer Gul Tuysuz reported from Istanbul . `` No lights . No electricity . '' The capital , Ankara , some 250 miles from Istanbul , also was affected . The outage extended to 45 of Turkey 's 81 provinces . The semiofficial Anadolu Agency quoted Energy Minister Taner Yildiz as saying the cause of the outage was unknown . Yildiz , speaking during a visit to Slovakia , said he could neither confirm nor deny that a cyberattack had triggered the blackout , the Anadolu Agency reported . Flightradar24 , which maps real-time flight data on the Internet , tweeted that the outage was `` affecting flights , '' and said 11 of its 16 air traffic monitoring systems receivers -- as distinct from the country 's air traffic control system -- were not working . The Turkish Electricity Transmission Co. blamed the outage on a problem with transmission lines , Anadolu Agency reported . The utility said an investigation was in progress , as were efforts to restore power , the news agency said . The outage began at 10:36 a.m. ( 3:36 a.m . ET ) . Nearly two hours later , according to Anadolu Agency , about 15 % of the power had been restored to Istanbul and Ankara , including in some subway stations . Power also was beginning to flow again to a number of provinces that had been cut off , the agency reported . By midafternoon , Yildiz said , 90 % of Istanbul 's power had been restored . `` Crowded places such as metro stations have been given electricity , and we believe the rest of the country should be fully powered shortly , '' he said . CNN '' s Gul Tuysuz contributed to this report from Istanbul .
Energy report says 90 % of Istanbul 's power has been restored . Turkish Prime Minister : All possible causes of corruption under investigation , including corruption .