Heavy fighting has broken out between opposition fighters and forces loyal to President Bashar al-Assad in a main district of Damascus that is home to several security installations, witnesses said.
The sound of heavy machine guns and rocket-propelled grenades echoed throughout the night from the western neighbourhood of al-Mezzeh, one of the most heavily guarded areas of the capital, residents told the Reuters news agency by telephone on Monday.
Syrian state television said three "terrorists" and a member of Syria's security forces were killed in the fighting.
Rami Abdel Rahman, the head of the UK-based Syrian Observatory for Human Rights (SOHR), earlier said that at least 18 security troops were wounded.
Lena, a member of the Revolutionary Leadership Council in Damascus, an opposition activist network, told Al Jazeera that residents in al-Mezzeh began hearing gunfire at about midnight.
"Some people came to al-Mezzeh and they are trying to attack residents. They are calling them names and taking them out of their houses ... people have left their homes. They are in the streets. The security forces are all around the place," she said.
Another witness who lives in the area said there was fighting near Hamada supermarket and the sound of explosions in nearby. "Security police have blocked several side streets and the street lighting has been cut off," she said.
Reporting from Beirut in neighbouring Lebanon, Al Jazeera's Rula Amin said: "Residents are telling us there was intense gunfire for hours. They could hear from loudspeakers the army and the security forces asking armed men to leave one of the buildings, Hamada supermarket.
"Al-Mezzeh is not geographically located in the heart of the capital but it's a very important neighbourhood. It is heavily guarded. There are a lot of high-ranking officials living in al-Mezzeh, in addition to the UN headquarters, embassies, and ambassadors," she said.
"This is taking place as the government claims they have control over the capital."
The latest fighting comes as Al Jazeera gained access to confidential documents prepared for Assad by his intelligence chiefs that give details of the regime's plans to contain the uprising and protect government strongholds.
The documents, running into hundreds of pages, point to a government desperate to keep control of the capital Damascus and include clear orders to stop protesters from getting into the city.
Elsewhere on Monday, the International Committee of the Red Cross (ICRC) said Russia's foreign minister voiced clear support for a plan for daily humanitarian ceasefires in Syria and promised Russia would press Assad's government to accept it.
Russian foreign Minister Sergei Lavrov "clearly agreed to and was supportive of" the idea of a daily two-hour cessation of hostilities to allow for life-saving aid operations, ICRC President Jakob Kellenberger told Reuters after talks with Lavrov in Moscow on Monday.
Asked whether Lavrov had promised that Russia would pressure Syria's government on the plan, Kellenberger said, "Yes, very much so".
The two sides issued no joint statement but ICRC officials said Kellenberger "received positive indications of support" from Lavrov.
The Red Cross has yet to receive permission from Syria to access all parts of the country affected by fighting. Moscow, an ally of Damascus, is seen as having a certain amount of influence on the Syrian leadership.
This came a day after Syria's opposition reported heavy raids by security forces and fighting with rebels in northern and southern provinces and suburbs of Damascus on Sunday.
A car bomb close to a state security office in Syria's second biggest city of Aleppo killed at least three people on Sunday, according to the SOHR.
Syrian state TV said that the"terrorist" explosion took place between two residential buildings in the al-Suleimaniya district, behind a post office.
In Damascus, crowds gathered for memorials to the 27 victims of Saturday's car bombs, which had targeted a customs office and air force intelligence headquarters.
State television also blamed "terrorists" for those attacks, but opposition activists said they doubted armed groups trying to bring down Assad would have the capacity to carry out such operations against his security institutions in Damascus.
The United Nations estimates that more than 8,000 people have died so far in the violence following the revolt against four decades of rule by the Assad family.
Syrian authorities say they are fighting insurgents who have so far killed more than 2,000 members of the security forces.