The Syrian capital Damascus was hit by a power cut late on Wednesday, shortly after an explosion near the international airport, residents said.
"The whole city just went dark," said a resident who lives in the centre of the city and asked to remain anonymous. She said that she could see the "major glow of a fire" near the airport and the sound of heavy machinegun fire.
The Syrian Observatory for Human Rights, a UK-based group that reports on abuses and battlefield developments using sources from both sides of Syria's civil war, said the explosion was caused by rebel artillery that hit a gas pipeline near the airport. It was not immediately clear why power was cut to the city.
The Observatory said the rebel shelling was aimed at the town of Ghasula, a few miles (km) from the airport.
Rebels have been trying to push into the capital, a stronghold of President Bashar al-Assad, whose family has ruled Syria for four decades.
More than 100,000 people have been killed during a pro-democracy uprising which started in March 2011.