UN chief Ban Ki-moon said Thursday that President Bashar al-Assad was not fulfilling his commitment to a ceasefire and pressed the Security Council to approve an expanded observer mission in Syria.
His remarks came as France also called for a more robust UN mission, warning that Syria was headed for civil war, and as the United States demanded tougher UN sanctions and an arms embargo on President Bashar al-Assad's regime.
The UN chief urged the council to take "early action" to send 300 unarmed observers to Syria to monitor a shaky ceasefire that started on April 12, but admitted that this "is not a decision without risk."
On a day when at least seven more civilians were reported killed by regime forces, he said there was "deeply troubling evidence" that the government was pursuing its deadly crackdown despite agreeing to halt violence.
"The past few days, in particular, have brought reports of renewed and escalating violence, including the shelling of civilian areas, grave abuses by government forces and attacks by armed groups," Ban said.
Earlier on Thursday, Syria and the United Nations signed a deal on a protocol for observers monitoring the ceasefire under a six-point plan agreed with UN-Arab League envoy Kofi Annan.
Damascus said it "comes within the framework of Syrian efforts aimed at making the Annan plan succeed and to facilitate the UN observer mission while respecting Syria's sovereignty."
In Geneva, Annan spokesman Ahmad Fawzi said the deal "outlines the functions of the observers as they fulfil their mandate in Syria and the tasks and responsibilities of the Syrian government in this regard."
Ban said that, "for the mission to succeed, we require the Syrian government's full cooperation, particularly in ensuring the full freedom of movement and unfettered access and safety and security of personnel."
Russia's UN envoy Vitaly Churkin said the council can "act very quickly" to pass a resolution allowing the full UN observer mission, and diplomats said one could be ready early next week.
"We believe that the Security Council should continue supporting Kofi Annan, should continue supporting his plan and continue supporting the secretary general," Churkin told reporters.
However, Western ambassadors were cautious.
German ambassador Peter Wittig said the Security Council must make sure the "conditions are right" before sending the enlarged force.
"The Assad government, of course, has to prove that its claim of support of the Annan plan is more than words. It has to stop the violence," he said.
Monitors say more than 11,000 people have been killed since the uprising against Assad's regime erupted in March 2011, with 127 dying since the truce came into force.
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In Paris, French Foreign Minister Alain Juppe said "the Annan plan is a guarantee of peace and freedom -- its failure the path to civil, even regional, war. Let us face our responsibility," he said.
He was speaking at a meeting of senior envoys, including US Secretary of State Hillary Clinton, seeking to pressure Assad's regime.
He said the "opposition has fulfilled its obligations under the Annan plan" and that "groups on the ground have respected the ceasefire" despite problems of coordination "made very hard by the provocations of the regime."
"We cannot say the same for the Syrian regime. It is pursuing without shame repressive tactics that have already left dozens more dead since the ceasefire was due to go into effect," he charged.
He called for tough sanctions against Damascus and for the small UN observer team already on the ground to be boosted to 300 or 400-strong and made "robust and credible" with land and air transport to cover the country.
For her part, Clinton said "we need to start moving very vigorously in the Security Council for a Chapter Seven sanctions resolution, including travel, financial sanctions, an arms embargo."
A Chapter Seven resolution, which can be imposed by the Security Council if member states think peace is threatened by an act of aggression, authorises foreign powers to take measures -- including military options.
But Clinton said Russia, which has a veto on the Security Council, would probably not allow such a motion to pass, and said states would have to seek further diplomatic and economic sanctions.
She said she had earlier met her Russian counterpart, Sergei Lavrov, in Brussels.
"He was, as usual, very intent upon laying responsibility on all sides, and in particular on the opposition, but he also has recognised that we are not in a static situation but a deteriorating one," she said.
Although he opted to stay away from the Paris meeting, Lavrov said Moscow was "honestly fulfilling its part" to end the violence.
"I have today called on my colleagues to abandon the rhetoric of self-fulfilling prophecies that Kofi Annan's plan will certainly fail," he said in Brussels.
"Before thinking about what to do in the future, we should do everything to make this plan successful."
The Paris meeting included foreign ministers and envoys from Germany, Saudi Arabia, Canada, Egypt, the UAE, Spain, the United States, Italy, Jordan, Kuwait, Morocco, Qatar, Britain, Tunisia, Turkey and the European Union.
The rebel Free Syrian Army, meanwhile, called for outside military intervention against the Damascus regime even without Security Council approval, in a video posted online on Thursday.
General Mustafa Ahmed al-Sheikh, who heads the FSA military council, called for "the formation of a military alliance of countries friendly to the Syrian people ... to carry out surgical strikes on key installations of the regime."