Blast strikes centre of Damascus
At least 13 people have been killed and scores injured in a powerful explosion which hit the heart of Damascus.
The blast came a day after Syria's prime minister narrowly escaped an assassination attempt in a heavily protected area of the city.
Residents said they heard a blast and saw thick, black smoke billowing from behind a group of buildings.
Gunfire was heard in the area immediately after the morning blast in the central district of Marjeh.
The nature of the blast was not clear but rebels fighting to topple president Bashar Assad's regime have increasingly targeted Damascus, the seat of his power.
Earlier At least 15 opposition fighters were killed in a battle with Syrian government troops for a military helicopter base in the country's north.
The British-based Observatory for Human Rights said fighting between rebels and president Bashar Assad's troops was the Mannagh base in the province of Aleppo.
Rebels have repeatedly targeted Assad's air bases around the country in their two-year campaign to topple his regime. More than 70,000 people have been killed since the conflict started in March 2011.