Syrian troops backed by Lebanese Hezbollah fighters and other pro-regime militiamen retook a major rebel enclave south of Damascus on Thursday, severing a key opposition supply line.
The recapture, reported by a monitoring group and state television, was part of a broader army campaign that has seen a string of towns in the area fall into regime hands.
Meanwhile, US Secretary of State John Kerry said in Amman he believed peace talks that had been proposed for the end of November could still be held in the coming weeks.
And in The Hague, the Organisation for the Prohibition of Chemical Weapons (OPCW) said inspectors had verified all but one of Syria's 23 declared chemical weapons sites.
The regime's recapture of Sbeineh comes nine days into a campaign aimed at cutting off one of the main rebel supply lines into southern Damascus, said the Syrian Observatory for Human Rights.
The Britain-based monitor said Sbeineh is one of the most important rebel position on the edges of Damascus.
"Rebels in southern Damascus have now had practically all their supply routes cut off," said Observatory chief Rami Abdel Rahman.
He said troops were backed "by fighters from Hezbollah," the powerful Lebanese Shiite movement, as well as "Syrian and non-Syrian Shiite fighters."
They have besieged a number of rebel-held suburbs, and UN officials have expressed concern over reports of trapped civilians and severe malnutrition.
"There are fears for the lives of civilians in Sbeineh. Experience tells us that the army may well execute civilians and put the blame on rebels," said Abdel Rahman.
Syrian state television said "terrorists" -- the regime's term for rebels -- were crushed in Sbeineh.
The takeover of Sbeineh comes a year into a suffocating army siege of the town and weeks after regime forces captured nearby Husseiniyeh, Ziabiyeh and Bweida.
Abdel Rahman said the army has been able to advance in part because of "divisions among the rebels."
Syria peace conference to slip by a week or so
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On the diplomatic front Kerry, struck an upbeat note in Jordan about deadlocked efforts to convene a peace conference on Syria.
He said he thought there would be some "clarity" in the coming days, and the peace conference "might be moved by a week or something like that."
Speaking at a press conference with Jordanian Foreign Minister Nasser Judeh, Kerry said part of the reason for the delay were plans by the Syrian opposition to meet on Saturday to discuss whether to attend.
"People are trying to respect their process appropriately," Kerry told reporters.
"So I'm confident that somewhere in the next days a date is going to be set," he said.
UN-Arab League special envoy Lakhdar Brahimi said earlier this week that a date for the talks to try and draw up a transition government and end the 31-month conflict could still not be agreed.
The fate of President Bashar al-Assad is crucial to the opposition which has insisted that his resignation be on the negotiating table -- a demand rejected by Damascus.
Meanwhile, the OPCW said its inspectors had verified all but one of Syria's declared chemical sites.
The group said Syrian personnel had visited one of two remaining sites that they could not visit for security reasons and filmed it with "sealed cameras."
OPCW and UN inspectors have until mid-2014 to destroy Syria's entire chemical arsenal and production facilities under the terms of a US-Russian deal to head off military strikes on Assad's regime.
"The verification was conducted with the support of sealed cameras used by Syrian personnel as per the inspection team’s guidance," the Hague-based OPCW said.
"The exact geographical location and the time of capture of the footage/images were fully authenticated," it said, adding that the site was near the northern city of Aleppo.
Syria has declared approximately 1,290 tonnes of chemical weapons and agents as well as 1,230 unfilled chemical munitions, meaning shells, rockets or mortars.
It has already destroyed 99 warheads and is expected to destroy 55 more, with Damascus facing a November 15 deadline to finalise the plan for the destruction of the chemical arsenal.
Elsewhere, French Foreign Minister Laurent Fabius said there was "fairly recent" proof that four French journalists abducted in Syria are alive.