BEIRUT A car bomb killed at least three people, wounded dozens and blew the windows out of buildings in north-eastern Damascus on Tuesday as rebel fighters stepped up attacks in the Syrian capital, pro-government television stations said.
The al-Ikhbariya news channel said the explosion went off near a military supply office. Addounia TV gave a preliminary toll of three people killed.
Both attributed the blast to a suicide bomber in a car.
But opposition activists in the area said it was not clear if it was by a bomb or a mortar round.
Video of the aftermath of the explosion broadcast on al-Ikhbariya showed a crater next to a road, about 2 by 2 metres (yards). Windows were blown out of nearby buildings but there was no footage of the remains of a car bomb or of any of the victims.
The British-based Syrian Observatory for Human Rights, which has a network of contacts in Syria, said civilians and soldiers were among the dead in the attack in the Rukn al-Din district.
Fighting between President Bashar al-Assad's forces and rebels has come closer to central Damascus in recent months. Once a bastion for Assad's forces, the capital has become a focal point of the two-year-old uprising that has devolved into civil war in which more than 70,000 people have been killed.
Rebels said on Monday they planned missile strikes on government and security sites in Damascus and told residents to leave the city to avoid being hit in a campaign they named "Operation Shaking the Fort".
Mortar bombs struck two schools and the compound of the state news agency SANA in the heart of the city on Tuesday. Another hit a hospital close to the Old City, a world heritage site dating back to the 3rd millennium B.C.
On Monday, rebels fired dozens of mortar rounds around the central Ummayad Square. The United Nations said it was pulling about half of its international staff after a mortar bomb landed near their hotel.
The Syrian military has responded with artillery attacks and air strikes on suburbs where rebels have based themselves amongst thousands of civilians trapped in the crossfire.
Rebels have made several other attempts to bring the fight to the heart of the capital but were pushed back to a ring of suburbs around the east and south of central Damascus.
But in recent months, street clashes, car bombs and mortar attacks have hit Damascus with rising intensity, showing that the rebels have become increasingly capable of striking at the city centre.