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Hillary Clinton, the US secretary of state, has condemned an attack on US ambassador Robert Ford, after his convoy was pelted with eggs and tomatoes by supporters of the Syrian president when the envoy and his colleagues met an opposition figure in Damascus.
"We condemn this unwarranted attack in the strongest possible terms," Clinton said on Thursday. "Ambassador Ford and his aides were conducting normal embassy business and this attempt to intimidate our diplomats through violence is wholly unjustified."
Jay Carney, the White House spokesman, said the mob was violent and seriously damaged embassy vehicles, but that Ford was unharmed.
"This is clearly part of a campaign to intimidate diplomats who are bearing witness to the brutality of the Assad regime," Carney said.
He added that the US would not recall Ford and urged the senate to "show its support and confirm [Ford] so he can continue his work".
Al Jazeera's Rosiland Jordan, reporting from Washington DC, said that with a media blackout in Syria, the US government believed it is necessary for its staff to remain in the country.
"It is incumbent upon Robert Ford, the ambassador, and his staff to remain in Damascus, to move around the country, to see what is happening between the government and those who are opposed to the government of Bashar al-Assad," our correspondent said.
Robert Ford, an outspoken critic of Assad's crackdown was "safely back at the US embassy" after Thursday's attack, Mark Toner, deputy spokesman at the US state department, said.
The diplomats were meeting Hassan Abdul-Azim, an opposition figure who has demanded an end to the crackdown as a condition for any dialogue with Assad.
Abdul-Azim said Ford was inside his office in the Syrian capital when the pro-Assad demonstrators tried to force their way in, breaking down some locked doors.
Office staff prevented them from storming in, but Ford was trapped inside for about three hours with up to 100 hostile government supporters outside.
Abdul-Azim said security forces arrived about an hour after the attack began.
"The mob was violent; it tried, unsuccessfully, to attack embassy personnel while they were inside several embassy vehicles, seriously damaging the vehicles in the process," Toner said.
"Syrian security officers finally assisted in securing a path from the ambassador's meeting for him and his aides back to the embassy."
In-depth coverage of escalating violence across Syria
For its part, the Syrian foreign ministry issued a statement accusing the US of "encouraging armed groups to practice violence against the Syrian Arab Army".
Ford has angered Damascus in the past, notably by visiting the flashpoint city of Hama with his French counterpart in July, ignoring a ban on Western diplomats from travelling outside the Damascus area.
Assad supporters assaulted both the French and US embassies soon after the visit, winning cheers from protesters who later faced a tank-led crackdown.
Assault on Rastan
Thursday's diplomatic incident took place as at least 27 people are reported to have been killed during a three-day siege by Syrian forces to recapture the central town of Rastan.
"The city is still under heavy shooting and shelling from the army's heavy weapons amid of news about major defections in the army trying to protect the people," the Local Co-ordination Committees said in a bulletin.
Reuters news agency reported that two of the 27 killed were military deserters and the rest were local residents, as the town came under a tank and helicopter-backed assault.
"Only today more than 40 were injured and 10 killed," an activist told Al Jazeera. "The whole city is besieged from all directions."
Seventeen additional deaths were reported in Homs, Avaaz, an international rights and advocacy group, said on Thursday, citing reports by citizen journalists in the city.
Battles are raging between the Syrian army and defected soldiers, who have formed what they call the "Khaled Batallion", Avaaz said.
UN split over sanctions
The US and the European Union have imposed sanctions on some Syrian officials, including Assad, because of the security crackdown that has left about 2,700 people, according to the UN.
However, the UN Security Council remains divided over whether to impose sanctions against Syria.
The council met again on Thursday behind closed doors to try to bridge divisions on what would be a first UN resolution condemning the government's six-month military crackdown and calling for inclusive political talks.
But the Europeans and Russia remained at odds over mentioning the possibility of sanctions against Assad's government.
The Europeans insist that if Syria doesn't comply with demands, including an immediate halt to violence and respect for human rights, the council should consider sanctions. But Russia's UN ambassador, Vitaly Churkin, said Moscow was opposed to sanctions.