Troops overran a rebel town and were locked in a second day of fierce fighting around Damascus on Thursday, a watchdog said, as Syria's opposition leader threatened to withdraw his peace initiative.
Muslim leaders at a summit in the Egyptian capital, meanwhile, worked on a draft resolution calling for "serious dialogue" between the opposition and government officials.
After a 16-day onslaught, troops retook Karnaz, a town on the strategic highway linking Damascus and Aleppo in the north, said Rami Abdel Rahman of the Syrian Observatory for Human Rights.
"(Rebel) fighters withdrew from Karnaz, which they seized in December last year, after heavy fighting and regular forces regained control," he told AFP.
Clashes and heavy shelling were reported in rebel strongholds around the capital for a second day as the army pressed a major offensive the Observatory said had killed at least 64 people on Wednesday.
Another six civilians -- three of them under 18 -- were killed when mortar rounds slammed into a bus garage in the northeastern district of Qaboon.
"The army is determined to crush terrorism around the capital and big cities, and over the past several days it has launched a qualitative operation and killed dozens of terrorists who dreamt of attacking and entering Damascus," said pro-regime newspaper Al-Watan.
The Observatory -- which relies on a vast network of sources on the ground for its information -- also reported regime shelling and clashes along a southern highway of the capital.
"Rebels attacked an army checkpoint overlooking the highway and now there are fierce clashes there," Marwan, an employee at a restaurant in the southern Midan district, told AFP by phone.
The Observatory also reported the arrival of military reinforcements at Daraya, an embattled southwestern suburb of Damascus that the army has bombarded for months.
On the outskirts of Damascus, troops pounded rebel positions across the east and in the south, the Observatory said, as clashes broke out around a military vehicle depot to the northeast.
These areas are among the strongest bastions of the rebellion against President Bashar al-Assad's regime, which is battling to suppress a revolt the UN says has killed more than 60,000 people.
The intensification of the fighting further dimmed prospects for peace talks suggested by opposition leader Ahmed Moaz al-Khatib.
The surprise gesture by Khatib, head of the opposition National Coalition, was welcomed by the United States and the Arab League, and was expected to receive the backing of the Organisation of Islamic Cooperation (OIC) meeting in Cairo.
But Damascus has so far ignored it and a key opposing faction has flatly rejected the initiative.
Khatib stepped up the pressure to engage in talks by setting the regime a deadline of Sunday to free all women held in Syrian prisons.
"The demand that the women are released means that if there is one single woman still in prison in Syria on Sunday, I consider that the regime has rejected my initiative," Khatib told BBC Arabic.
The Syrian National Council, the main component of the Coalition, has rejected the possibility of any talks, saying it is committed to ousting Assad's regime and protecting the revolution.
A draft OIC resolution calls for "serious dialogue" between the Syrian opposition and government officials "not directly involved in oppression."
Among the leaders taking part in Cairo, Iranian President Mahmoud Ahmadinejad said he wanted his allies in the Syrian regime to negotiate with the opposition for the staging of a free election, in an interview with Egyptian state television.
The conflict flared after Assad's regime launched a bloody crackdown on democracy protests that erupted in mid-March 2011.
It has seen hundreds of thousands flee Syria, and Doctors Without Borders (MSF) said more than half of the estimated 300,000 refugees in Lebanon were not receiving the medical treatment they need due to high costs.