A firefight is reported to have erupted in Syria’s capital, Damascus, between the rebel Free Syria Army and the forces of President Bashar al-Assad.
Witnesses say the sound of machine-guns and rocket-propelled grenades can be heard from the district of al-Mezze.
The neighbourhood, in the centre of Damascus, is home to several security facilities and is one of the most heavily guarded parts of the capital.
In January the Free Syria Army briefly seized several Damascus suburbs.
Al-Mezze has been the scene of large anti-government protests.
“There is fighting near Hamada supermarket and the sound of explosions there and elsewhere in the neighbourhood,” a resident told Reuters news agency.
“Security police have blocked several side streets and the street lighting has been cut off.”
Opposition activist Amer al Sadeq told the BBC’s World Today programme he had spoken to a contact in al-Mezze who reported four blasts within five minutes and then heavy gunfire.
The incident follows bomb blasts in Damascus and the northern city of Aleppo over the weekend.
On Sunday a car bomb exploded in Aleppo, killing at least two people and injuring 30 others.
A day earlier, at least 27 people were reported to have been killed and 97 wounded in two explosions in the capital.
State TV described the blasts as “terrorist” attacks.
However, activists have accused the authorities of staging incidents to discredit opposition groups.
In another development, the UK-based Syrian Observatory for Human Rights said security forces beat and arrested senior opposition figure Mohammed Sayyed Rassas on Sunday.
Mr Rassas, a leader of the National Co-ordinating Body for Democratic Change (NCB), had been taking part in a protest march in Damascus, the group said.
President Assad is trying to quell an increasingly armed rebellion that sprang from a fierce crackdown on peaceful pro-democracy protests a year ago.
The UN estimates that more than 8,000 people have died in the clashes.
President Assad insists his troops are fighting “armed gangs” seeking to destabilise Syria.
