Elite troops backed by tanks massed round the Syrian protest city of Homs on Wednesday as Washington worked on a UN Security Council draft resolution demanding humanitarian access to trapped civilians.
China said it backed sending international aid as diplomats said the new text being drawn up by Washington focused on getting relief into cities under assault in a bid to avoid a third set of vetoes from Beijing and Moscow.
Washington said it opposed sending weapons to opponents of President Bashar al-Assad for fear that Al-Qaeda was exploiting the more than 11-month uprising against his regime after key US ally Saudi Arabia voiced strong support for arming the rebels.
Regime forces kept up their pounding of rebel neighbourhoods in Homs -- under assault for 26 days -- as efforts to bring wounded French journalist Edith Bouvier to safety continued after her British colleague Paul Conroy was successfully smuggled out to Lebanon.
Activists on the ground in Syria's third-largest city said that elite troops of the Fourth Armoured Division under the command of Assad's brother Maher had taken up position with their armour around the rebel stronghold of Baba Amr.
Hadi Abdullah of the Syrian Revolution General Commission told AFP by telephone that it was a likely prelude to a final assault.
Access to Homs has now been completely sealed off, according to commanders of the rebel Free Syrian Army, who said the regular army had also destroyed a tunnel.
Efforts to bring out Le Figaro journalist Bouvier, who has multiple fractures, continued after French President Nicolas Sarkozy went back on an earlier statement that she had been rescued from Baba Amr.
A management source at Le Figaro told AFP that Bouvier, 31, was "not in Lebanon but still in Syria."
British freelancer Conroy was at the British embassy in Beirut "in good condition" after being smuggled out of Syria on Monday night, a Lebanese official told AFP.
In London, the Foreign Office in London said he was "receiving full consular assistance from our embassy."
Thirteen Syrian activists were killed trying to help the Western journalists and to bring in aid to Baba Amr, international activist group Avaaz said.
At the United Nations, diplomats said that Washington had begun work on a new draft Security Council resolution demanding humanitarian access to besieged protest cities.
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"At the moment there are just tentative contacts on the resolution," one Security Council diplomat said.
"This resolution will concentrate on humanitarian access to the cities, but it will indicate that the government is the cause of the crisis," said another.
Western nations hope that focusing on the humanitarian crisis will persuade Russia and China not to use their veto powers as permanent members of the 15-member council as they did last October and again in early February.
French foreign ministry spokesman Bernard Valero said the text calls for a halt to violence and "immediate, unhindered access for humanitarian aid to the most threatened sites and the most vulnerable populations."
French Foreign Minister Alain Juppe said: "I solemnly appeal to Russia and China that they do not block this new resolution at the Security Council."
Work on the new draft started after Arab and Western governments met for an inaugural Friends of Syria meeting in Tunis last week, diplomats said.
"We really hope that by concentrating on an appeal for an end to the violence and getting humanitarian access we can get the support of everyone, including Russia and China," said one Western envoy.
Chinese Foreign Minister Yang Jiechi has told Arab League chief Nabil al-Arabi that international humanitarian aid should be allowed into Syria, Chinese state media said.
"The international community should create favourable conditions in this regard and provide humanitarian aid to Syria," the state Xinhua news agency quoted Yang as saying.
UN political chief B. Lynn Pascoe told the Security Council "well over 7,500" people have now been killed Syria since protests against Assad's regime first erupted in March last year.
The White House said that Al-Qaeda's efforts to take advantage of violence in Syria meant it was no time to send arms to Assad's opponents as advocated by Saudi Arabia at the Friends of Syria meeting.
"Now is not the time to further militarise the situation in Syria," said White House spokesman Jay Carney.
"Without getting into assessments of our intelligence capabilities, I would simply say that we are aware of the fact that Al-Qaeda and other extremists are seeking to take advantage of the situation created by Assad's brutal assault on the opposition," he said.
Al-Qaeda leader Ayman al-Zawahiri has expressed backing for the Syrian rebels although they have disavowed his support.