The opposition Free Syrian Army (FSA) has given the Syrian government a deadline of noon Friday to observe a UN ceasefire that calls for government forces to withdraw from residential areas, the BBC reported.
The FSA said that if there was no response, it would no longer consider itself bound by the peace plan – and would take what it called "courageous decisions."
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Western countries are demanding increased pressure on Syria, after a UN Security Council meeting was held yesterday to discuss violence in the country.
The US ambassador to the UN, Susan Rice, said prospects for a political solution were almost non-existent following ongoing violence, and that the Security Council must discuss new action, Agence France Presse reported.
Both France and Germany called for a strengthening of sanctions, but Russia, Syria's ally, said it would not accept a new resolution.
The UN meeting came after the bodies of another 13 people – who had been killed "execution-style" – were found near Deir Ezzor, in eastern Syria.
Meanwhile, Hazem Chehabi, a Syrian honorary consul in the United States, resigned in protest after last week's massacre in the central town of Houla, AFP reported.
Activists say more than 100 people, including dozens of children, and in some cases, entire families, were killed in an assault on the town by pro-government forces.
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Chehabi, who had held the post of honorary consul for 18 years, told National Public Radio:
"You get to a point where your silence or your inaction becomes ethically and morally unacceptable.”
Chehabi said the Houla massacre was a “tipping point” and beyond the point at which “one could not justify remaining silent."