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A firefight has erupted in Damascus, in one of the fiercest clashes in the Syrian capital since the uprising against President Bashar al-Assad's rule began.
Witnesses say machine-guns and rocket-propelled grenades were heard from the heavily guarded district of al-Mezze, which hosts several security buildings.
Syrian TV said three "terrorists" and a security force member had been killed.
The UN estimates more than 8,000 people have died in the year-long uprising.
Meanwhile, a team of experts sent by special UN and Arab League envoy Kofi Annan has now arrived in Syria to discuss ceasefire and monitoring plans, AFP news agency reports.
And in Moscow, the head of the Red Cross said that Russia had reacted "positively" to his call for a daily two-hour cessation of hostilities in Syria.
Al-Mezze has previously been the scene of large anti-government protests.
One resident told Reuters news agency there was "fighting near Hamada supermarket and the sound of explosions there and elsewhere in the neighbourhood".
He said security police blocked side streets and cut off the street lighting.
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 UK-based Syrian Observatory for Human Rights called the fighting "the most violent of its kind and closest to security centres in Damascus since the revolution began", adding that 18 government troops had been injured.
It said a cell of rebel fighters had fired a rocket-propelled grenade at the home of a leading army officer, but this has not been confirmed.
The gunfire continued into Monday morning but is now over.
One al-Mezze resident told AFP: "We were very scared but now the roads are clear and stores are open."
State television said that in addition to the dead, several people on both sides were injured.
In January, the rebel Free Syria Army briefly seized several Damascus suburbs.
The latest incident follows bomb blasts in Damascus and the northern city of Aleppo over the weekend.
The car bomb that exploded in Aleppo on Sunday killed at least two people and injured 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.
Reuters news agency on Monday reported residents of the eastern city of Deir Ezzor as saying that dozens of tanks had entered the city to try to dislodge Free Syrian Army rebels.
On Monday, a team of experts arrived in Syria to press Mr Annan's proposals for a ceasefire and monitoring.
Annan spokesman Ahmad Fawzi told AFP: "There are five people with expertise in peacekeeping and mediation. They will be staying for as long as they are making progress to reach agreement on practical steps to implement Mr Annan's proposals."
Meanwhile, the head of the International Committee of the Red Cross (ICRC), Jakob Kellenberger, travelled to Moscow to meet Foreign Minister Sergei Lavrov.
Mr Lavrov gave "positive indications of support... for the initiative of a two-hour cessation of fighting on a daily basis", a Red Cross spokesman said.
The ICRC says the pause is needed for the evacuation of the wounded and to allow in food and medicine.
Mr Kellenberger added: "I would like to note with satisfaction and gratitude that Sergei Lavrov shares our concern about these problems."
Russia is a key ally of Syria and, along with China, has thwarted attempts to form a UN resolution condemning the repression.
President Assad is trying to quell an increasingly armed rebellion that sprang from a fierce crackdown on peaceful pro-democracy protests a year ago.
He insists his troops are fighting "armed gangs" seeking to destabilise Syria.