The Syrian army has moved to retake control of Damascus suburbs from rebel forces, activists say.
They say troops backed by tanks shelled rebel-held areas to the east and north.
At least 26 people have reportedly been killed this weekend in what activists say is the fiercest fighting around the capital during the 10 month-uprising.
Across Syria, activists said a total of about 60 people were killed on Sunday - a day after the Arab League suspended its month-old monitoring mission.
The government said at least 16 soldiers died in two attacks by armed rebels.
Reports say troops loyal to Syrian President Bashar al-Assad stormed the eastern Damascus suburb of Ghouta, where large anti-government protests have taken place.
One activist, Kamal, told Reuters news agency the rebel Free Syrian Army had made a tactical withdrawal.
"Regime forces have re-occupied the suburbs and started making house-to-house arrests," he said.
The latest army offensive started on Saturday in suburbs where the Free Syrian Army had taken up positions - including Kfar Batna, Saqba, Jisreen, and Arbeen.
Activists said more than 2,000 troops and 50 tanks joined the operation on Sunday, barely 5km (three miles) from the city centre.
"It's urban war. There are bodies in the street," said one activist, speaking from Kfar Batna.
One activist in the eastern Damascus suburb of Saqba said mosques there had been turned into field hospitals.
"They cut off the electricity," the activist told Reuters news agency. "Petrol stations are empty and the army is preventing people from leaving to get fuel for generators or heating."
There were similar reports from the mountain town of Rankous, about 30km (18 miles) to the north.
Anti-government groups said it had become a "disaster zone" with columns of smoke rising from homes hit by shellfire.
Syria's state-run Sana news agency said a roadside bomb planted by an "armed terrorist group" had struck a bus carrying troops near the Damascus suburb of Sahnaya on Sunday, killing six.
Surge in violence
Rami Abdul Rahman, head of the UK-based Syrian Observatory for Human Rights, said the fighting was "the most intense near the capital since the uprising began".
"The Syrian regime is trying to finish the uprising militarily now that the case is being taken to the United Nations."
Such reports are difficult to verify because of government restrictions on the media.
On Saturday the Arab League announced it was halting its observer mission for the time being, because of the ongoing violence.
The BBC's Jim Muir in neighbouring Lebanon says both the upsurge and the suspension mean that even more attention will be focused on the UN Security Council's efforts next week to get a tough resolution on Syria.
In December the UN said more than 5,000 people had been killed since protests against the government of President Bashar al-Assad first erupted last March.
Syrian officials say government troops are fighting "terrorist" groups and about 2,000 members of the security forces have been killed in the unrest.
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