Government and Hezbollah forces controlled most of Qusair Wednesday, giving the regime of President Bashar Assad new momentum in the civil war, rebels said.
A member of the main exile opposition group, the Syrian National Coalition, said after mediation brokered by Lebanese politician Walid Jumblatt, U.N. officials delivered the message Assad had agreed to allow the injured to leave Qusair on condition "armed gangs" leave and relinquish the key crossroads city, The New York Times reported.
Inside Qusair, ammunition was low, rebel reinforcements couldn't pierce the government's perimeter and the wounded could not be evacuated as Hezbollah fighters attacked the city backed by government airstrikes and artillery bombardments, witnesses said.
"The Syrian government and other parties to this conflict must fulfill their obligations under international human rights and humanitarian law by immediately allowing neutral, impartial humanitarian organizations, including U.N. agencies, safe access to evacuate the wounded and provide lifesaving medical treatment and supplies, Carney said.
Carney said it was "clear that the regime is unable to contest the opposition's control of a place like Qusayr on their own, and that is why they are dependent on Hezbollah and Iran to do their work for them.
"And as I've said before, the fact that a regime like Assad has its partners in tyranny here -- Hezbollah and Iran -- says a great deal about their intentions and the fact that Assad's principal concern has been his own grasp on power, not his own people -- people that he's butchered."
The Syrian Network for Human Rights said Wednesday more than 1,000 injured civilians are trapped in Qusair, about 600 of them unable to walk.
The organization appealed to "all formal and informal organizations in the world for urgent intervention to save their lives."
The United Nations expressed concern about a humanitarian crisis in Qusair after the government and Hezbollah refused to allow Red Crescent humanitarian workers into the city before military operations ended.
"What happened to all the fighters who were on their way to Qusair to support us?" Ammar, an anti-government activist identified only by his first name for safety, asked the Times.
Syrian media and military officers depicted the development as a potential turning point in the civil war that began as peaceful anti-government protests in March 2011.
"He who controls Qusair controls the center of the country and he who controls the center of the country controls the whole of Syria," Brig. Gen. Yahya Suleiman told Mayadeen television.
Opposition forces vowed to fight, the Times said.
"Yes my brothers, it is one round that we lost," the opposition Qusair Coordinating Committee posted on its Facebook page. "But war is a drawn out competition."
The British Foreign Office said tests reveal the nerve agent sarin was used during the civil war while the French foreign minister said he was certain sarin was used by the Assad regime, The Independent reported.
France's Laurent Fabius' statement seemed to clarify what several organizations had suggested for months -- that chemical weapons have been used on multiple occasions.
"These tests show the presence of sarin in various samples in our possession," Fabius said in a statement, adding the results were passed along to the United Nations. "France is certain that sarin gas was used several times in Syria in limited areas."
In an interview with France 2 television, Fabius said there was "no doubt" the toxic chemical was used by the Assad regime.
Britain's statement did not attribute use of sarin to either side. The Foreign Office said the presence of sarin was confirmed but didn't indicate when or where the samples were obtained.
The Tuesday U.N. report on human rights abuses in the civil war suggested troops loyal to Assad and a number of rebel groups were responsible for using chemical weapons.