“Syria has suffered a massive power blackout across the country due to “unknown reasons”, state media said.
Officials were cited as saying power had been cut in all provinces and teams were trying to determine the cause.
The electricity ministry said power was being restored and service would resume by midnight (22:00 GMT), TV reported.
In most parts of war-torn Syria, electricity is already available only two to four hours a day, if at all. However, nationwide blackouts are rare.
Meanwhile, the UN’s special envoy said a partial truce that began on Saturday was holding but remained fragile.
Staffan de Mistura told reporters in Geneva that violence had been “greatly reduced”, despite incidents in the provinces of Homs, Hama, Latakia and Damascus. “Success is not guaranteed but progress is visible,” he added.
Both the opposition and the government have accused each other of violating the cessation of hostilities agreement brokered by the US and Russia, which does not include the jihadist groups Islamic State (IS) and al-Nusra Front.”