US Secretary of State John Kerry said this week that Security Council action could also be taken over delays in moving Syria's deadliest chemicals out of the country.
The fate of an estimated three million people trapped in areas where there is fighting, or blockaded by government or rebel guns, will be the immediate focus.
While the Geneva talks went ahead, the UN had trucks carrying enough food for more than 2,500 people trapped in the Old City district of Homs.
The Syrian government refused to allow the convoy in, despite pressure from UN-Arab League peace envoy Lakhdar Brahimi at the talks that ended Friday.
Assad's negotiators only offered to let women and children out, but diplomats said this would have left the men remaining open to a government massacre.
"I am extremely concerned that, while the discussions continue to try and find a political solution to end the crisis, ordinary men, women and children are dying needlessly across the country and others are desperate for want of food, clean water or medical care," said UN humanitarian chief Valerie Amos.
Other towns are in worse condition than Homs. No aid has entered East Ghouta near Damascus for more than a year, and UN leader Ban Ki-moon denounced the situation as "shocking."
In talks with Turkish Foreign Minister Ahmet Davutoglu, Kerry urged the regime to increase humanitarian access.
The pair agreed that "the delay in providing access for convoys into Homs and other besieged areas was simply unacceptable," a senior State Department official said.
Security Council weighs more action
Arab nations at the UN have written one draft Security Council resolution on the humanitarian crisis. Council members Australia and Luxembourg have another. And diplomats said work has started on merging the two.
"There is a compelling case for bringing the humanitarian situation back under discussion in the Security Council," said British Foreign Secretary William Hague.
A decision on when to press the resolution is not likely until after Amos chairs a meeting on the Syrian crisis in Rome on Monday.
Much will depend on whether Russia can persuade its Syrian ally to open up Homs, diplomats said.
US warnings over Syria's chemical weapons will turn the screws on Assad, diplomats and analysts said.
Sources close to the Organisation for the Prohibition of Chemical Weapons say that less than four percent of its most dangerous chemicals have been moved.
All the Class A chemicals were meant to be moved by February 5 under a Russia-US deal that halted a US threat to carry out military strikes on Syria last year.
"We now know that the Assad regime is not moving as rapidly as it promised to move the chemical weapons out of Syria," said Kerry.
He highlighted that Security Council Resolution 2118 on the chemical deal "makes it clear that if there are issues of non-compliance, they will be referred to the Security Council for Chapter VII compliance purposes."
Russia, which has already used its veto power to block three council resolutions stepping up pressure on Assad in the nearly four years of the conflict, would almost certainly not allow sanctions this time.
But diplomats said that pressure is mounting on Russia to try to get a concession out of Assad.
The head of the UN-OPCW mission, Sigrid Kaag, is due to brief the Security Council on the delays Thursday.
"I don't think we are quite at the stage of non-compliance, but it will be important what Sigrid Kaag says about whether she thinks the delays are deliberately political motivated," said one Western official.
Syria has blamed security concerns and bad weather for the delays. Western diplomats say neither excuse can be used now.
There is "undoubtedly" a link between the failed Geneva talks and the new diplomatic offensive, said Andrew Tabler, a Syria specialist at the Washington Institute for Near East Policy.
"All this is leverage on Assad and it pressures the Russians to do something," he said.
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The fate of an estimated three million people trapped in areas where there is fighting, or blockaded by government or rebel guns, will be the immediate focus.
While the Geneva talks went ahead, the UN had trucks carrying enough food for more than 2,500 people trapped in the Old City district of Homs.
The Syrian government refused to allow the convoy in, despite pressure from UN-Arab League peace envoy Lakhdar Brahimi at the talks that ended Friday.
Assad's negotiators only offered to let women and children out, but diplomats said this would have left the men remaining open to a government massacre.
"I am extremely concerned that, while the discussions continue to try and find a political solution to end the crisis, ordinary men, women and children are dying needlessly across the country and others are desperate for want of food, clean water or medical care," said UN humanitarian chief Valerie Amos.
Other towns are in worse condition than Homs. No aid has entered East Ghouta near Damascus for more than a year, and UN leader Ban Ki-moon denounced the situation as "shocking."
In talks with Turkish Foreign Minister Ahmet Davutoglu, Kerry urged the regime to increase humanitarian access.
The pair agreed that "the delay in providing access for convoys into Homs and other besieged areas was simply unacceptable," a senior State Department official said.
Security Council weighs more action
Arab nations at the UN have written one draft Security Council resolution on the humanitarian crisis. Council members Australia and Luxembourg have another. And diplomats said work has started on merging the two.
"There is a compelling case for bringing the humanitarian situation back under discussion in the Security Council," said British Foreign Secretary William Hague.
A decision on when to press the resolution is not likely until after Amos chairs a meeting on the Syrian crisis in Rome on Monday.
Much will depend on whether Russia can persuade its Syrian ally to open up Homs, diplomats said.
US warnings over Syria's chemical weapons will turn the screws on Assad, diplomats and analysts said.
Sources close to the Organisation for the Prohibition of Chemical Weapons say that less than four percent of its most dangerous chemicals have been moved.
All the Class A chemicals were meant to be moved by February 5 under a Russia-US deal that halted a US threat to carry out military strikes on Syria last year.
"We now know that the Assad regime is not moving as rapidly as it promised to move the chemical weapons out of Syria," said Kerry.
He highlighted that Security Council Resolution 2118 on the chemical deal "makes it clear that if there are issues of non-compliance, they will be referred to the Security Council for Chapter VII compliance purposes."
Russia, which has already used its veto power to block three council resolutions stepping up pressure on Assad in the nearly four years of the conflict, would almost certainly not allow sanctions this time.
But diplomats said that pressure is mounting on Russia to try to get a concession out of Assad.
The head of the UN-OPCW mission, Sigrid Kaag, is due to brief the Security Council on the delays Thursday.
"I don't think we are quite at the stage of non-compliance, but it will be important what Sigrid Kaag says about whether she thinks the delays are deliberately political motivated," said one Western official.
Syria has blamed security concerns and bad weather for the delays. Western diplomats say neither excuse can be used now.
There is "undoubtedly" a link between the failed Geneva talks and the new diplomatic offensive, said Andrew Tabler, a Syria specialist at the Washington Institute for Near East Policy.
"All this is leverage on Assad and it pressures the Russians to do something," he said.
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