Syrian regime forces have shelled two central Damascus districts before troops backed by tanks swept through to carry out house-to-house raids, killing at least 35 suspected rebels, in a major flare-up of fighting in the Syrian capital, activists said.
The capital is one of many fronts President Bashar Assad's regime is struggling to contain as the 17-month-old rebellion against his rule gains strength.
Government forces are also engaged in a major battle for control of the northern city of Aleppo as well as smaller-scale operations in the country's south, east and centre.
On the diplomatic front, a senior UN official said Iran's arms supplies to Syria violated UN sanctions. France also indicated it has provided the rebels with communication and protection equipment but cautioned against foreign intervention without a UN mandate.
A prominent opposition figure, meanwhile, rejected as "more lies" comments by a senior Syrian official that Damascus would be willing to discuss Assad's resignation but only after the opposition agreed to join in negotiating a peaceful settlement.
"As for his resignation, making his resignation a condition for dialogue effectively makes holding such a dialogue impossible," said Deputy Foreign Minister Qadri Jamil. "During the negotiating process any issues can be discussed, and we are ready to discuss even this issue."
Adib Shishakly of the Syrian National Council, a key umbrella opposition group, said: "It's the first time that we hear such talk, but it's difficult to believe. We have grown accustomed to the regime's lies."
Earlier, regime forces in Damascus rained mortar shells on the upscale Kafar Soussa area - home to the foreign ministry, the prime minister's office and several foreign embassies - and adjacent Nahr Eishah, activists said.
Government troops appeared to be shelling the districts from the Qasioun mountain overlooking the capital, a Damascus resident said.
The attacks may have been designed to kill or capture rebel mortar teams who have used the two neighbourhoods in recent days to target the city's strategically located Mazzeh military airport, activists said.