Security forces are also continuing their efforts to crush anti-government protests in the cities of Homs and Deraa, and the coastal town of Baniyas.
The EU meanwhile imposed an arms ban and sanctions against officials.
In a statement, the bloc said it was banning the shipment to Syria of "arms and equipment that could be used for internal repression".
The 13 officials are banned from travelling anywhere in the 27-nation union and have had their assets in EU countries frozen.
Communications cut Foreign journalists have not been allowed to enter Syria, so reports from the country are difficult to verify independently.
On Monday morning, reports from activist websites said that the suburb of Muadhamiya had been cut off by the army at dawn. Electricity and telephone lines were cut off.
Soldiers and tanks were deployed on the main streets and outside the al-Rawda and al-Omari mosques, while snipers were positioned on tall buildings, the websites added.
An activist in Damascus told the BBC that at least three civilians had been killed and many others wounded inside the town. About 200 people had been arrested, he said.
"Military and security forces have used deadly force against people inside the city, and they want to arrest specific people... who are the leaders of [the] protests," he added.
People trying to leave or enter Muadhamiya are having their ID cards checked, sources said.
Gunfire was also reported in nearby Darayya. Both towns are not far from the Mezze military airport and the Sumariya army barracks.
Meanwhile, more security forces were reported to have moved into the central city of Homs, north of Damascus, where troops backed by tanks have been raiding houses and arresting people since Saturday night.
On Monday, a resident told the BBC that the security forces were dividing up the city to prevent people joining any mass protests.
"There is the sound of tank-fire and gunfire coming from the outskirts of the city. Last night, there was continuous gunfire for several hours," he said. "There is no electricity or mobile phone coverage."
The UK-based Syrian Observatory for Human Rights said on Sunday that the areas of Bab Sebaa, Bab Amro and Tal al-Sour were under "total siege", and that hundreds had been arrested. The number of casualties was unknown, it added.
Some 15 people were said to have been shot dead in Homs on Friday after taking part in demonstrations following Friday prayers.We cannot stay for a long time faced with these guns”
"We cannot stay for a long time faced with these guns - somebody from... other nations, from Turkey, should [do] something," the Homs resident added. "This government should protect [its people], not kill them."Correspondents say a key tactic of the authorities has been to isolate and intimidate people in areas where anti-government resistance is strongest.
The army says operations against "armed terrorists" are continuing.
Six soldiers and police had been killed and others wounded on Sunday in Homs, Baniyas and villages around the southern city of Deraa, it added.
Dissident charged Activists say more than 250 people have been arrested in Baniyas, including protest organisers, women and a 10-year-old boy. At least six protesters were killed on Saturday, they added, including four women taking part in a small all-women rally.
"Hundreds of women, despite the presence of the security agents and the military, are going out on the streets to demand those arrested be released," Rami Abdul Rahman of the Syrian Observatory for Human Rights told the AFP news agency.
Earlier, water, electricity and telephone lines were cut in the town. Tanks and other armoured vehicles were also deployed on roads leading to Baniyas and surrounding towns, reliable sources told the BBC.
In Deraa, which has been under military occupation for two weeks and where scores of protesters have been killed, residents were allowed out for a few hours to buy supplies before a curfew was imposed.
A witness also told the Reuters news agency that security forces had killed two protesters in the eastern town of Deir al-Zour.
Meanwhile, Syrian state TV showed pictures of a minibus in which 10 Syrian workers coming home from Lebanon were said to have died when it was ambushed near Homs by gunmen early on Sunday morning.
Bashar al-Assad Syrian PresidentThe crisis will pass and end, and the question of administrative, political and press reforms will advance”
The Syrian Observatory for Human Rights says 621 civilians and 120 security personnel have been killed since demonstrations pro-democracy protests began in March. Another Syrian rights group, Sawasiah, says more than 800 civilians have been killed.The government disputes the civilian toll and says about 100 soldiers have been killed.
The unrest poses the most serious challenge to President Bashar al-Assad since he succeeded his father, Hafez, in 2000.
Mr Assad was quoted by the al-Watan newspaper on Monday as saying he was confident the unrest would be overcome.
"The crisis will pass and end, and the question of administrative, political and press reforms will advance," he said.
Syrians must "consolidate national unity because the nation is the mother of all of us and we need to unite in the face of this plot," he added.