Syria's military pursued a crackdown on rebels on several fronts on Monday, days after eliminating an opposition bastion in the central city of Homs following a 26-day siege, activists said.
Troops kept the Red Cross out of the wrecked Homs district of Baba Amr for a fourth day and foreign mediators sought to end year-long violence as more civilians fled to nearby Lebanon.
U.S. Senator John McCain said the United States should lead an international effort to protect key population centres in Syria through air strikes on President Bashar al-Assad's forces.
The ultimate goal of air strikes should be to establish and defend safe havens in Syria, especially in the north, in which opposition forces can organize and plan their political and military activities against Assad, McCain, an influential Republican who previously has called for arming the Syrian opposition, said in remarks on the Senate floor.
The United Nations says more than 7,500 civilians have died in Syria's crackdown on protests against Assad's government.
Braving army patrols and winter weather, hundreds of Syrians crossed into Lebanon in the past 24 hours to escape the heaviest shelling of their border towns since the uprising against Assad began last March.
In the hillside town of Arsal in Lebanon's Bekaa Valley, residents said 100 to 150 families arrived from Syria on Sunday -- one of the biggest refugee influxes so far.
Families trekked on foot through snow-capped hills to safety, but many others were caught, one refugee told Reuters.
My house was bombed and a giant hole was left in one side of the house, said a 21-year-old man in a black leather jacket and black-and-white scarf from the Syrian town of Qusair.
Syria has so far brushed off international pressure to halt its violent response to an uprising that was inspired by revolts that have toppled four Arab autocrats in the past 12 months.
The U.N.-Arab League special envoy to Syria, Kofi Annan, will travel to Damascus on Saturday for what would be his first visit since he was named to the post last month.
The Syrian state news agency SANA said the government welcomed his visit and had accepted one by U.N. humanitarian chief Valerie Amos, who was denied entry to Syria last week.
Russian Foreign Minister Sergei Lavrov said he hoped a meeting with Arab counterparts in Cairo on Saturday would bring the world closer to agreement on how to end the bloodshed, but gave no sign Moscow would stop protecting its old ally Assad.
Moscow, along with China, has been widely condemned in the West for vetoing a U.N. Security Council resolution that would have backed an Arab League call for Assad to step down as part of a political transition.
Some Western powers expressed hope that Vladimir Putin's election as Russian president on Sunday might provide an opening for a change in policy.
British Prime Minister David Cameron called Putin on Monday to discuss Syria and other matters of international concern, a spokesman for Cameron said.
The Prime Minister and Mr Putin also discussed Syria and the need for united international action to bring an end to the violence and prevent the situation deteriorating into civil war, the spokesman said.
French Foreign Minister Alain Juppe said Moscow had isolated itself with regard to the Arab world and the international community following its stance on Syria.
We can understand that during the election period the moment wasn't right to make the Russian position evolve, Juppe said.
I would like therefore that Russia's position changes and I am ready to discuss it with the Foreign Minister, the same one if he is kept in his post, or his successor if he is changed.
Juppe said he did not think it was impossible to get a U.N. Security Council resolution and that this was something that Paris would be working on in the coming days.
Initial signals from Russia, though, were that diplomacy still has some way to go before a resolution will pass muster.
Russian Deputy Foreign Minister Gennady Gatilov said on Monday that a new U.S.-drafted resolution on Syria is only slightly different from a draft Russia vetoed last month and needs to be more balanced.
Western envoys at the United Nations said last week that the United States had drafted an outline for a new resolution demanding access for humanitarian aid workers in besieged Syrian towns and an end to the violence there.
The new U.S. draft U.N. Security Council resolution on Syria is a slightly renewed version of the previous vetoed document. It needs to be significantly balanced, Gatilov said on Twitter.
Assad has said his political reforms will ensure a multi-party election within three months based on a new constitution, but the opposition says the bloodshed makes a mockery of such plans.
CHANGE OF LEADERSHIP
While European Union foreign policy chief Catherine Ashton urged Russia to help get humanitarian aid to Homs, she asked Moscow to recognise the need for a new leadership in Syria.
China, which has twice joined Russia in blocking U.N. Security Council action against Syria, said it would send its envoy, Li Huaxin, to Damascus on Tuesday.
China still maintains that a political solution offers the fundamental escape from the Syrian crisis, Foreign Ministry spokesman Liu Weimin said in Beijing.
Canada imposed fresh sanctions on Syria on Monday, banning all dealings with the central bank and seven cabinet ministers as part of a campaign to stop President Bashar al-Assad's crackdown against rebels.
The measures also prohibit the provision or acquisition of financial or other related services to or from anyone in Syria or those acting on Syria's behalf.
In Syria, hundreds of troops fanned out in Deraa on a scale not seen for months following rebel attacks that were also unusually extensive, a resident said. At least one person was killed.
Outgunned rebels have multiplied hit-and-run assaults across Syria in the last few days to signal their defiance after the military overran the shattered Baba Amr district of Homs.
A bomb explosion hit an oil pipeline in Syria's eastern province of Deir al-Zor on Monday as Syrian troops began a sweep in the region, opposition activists said.
Syrian armoured forces recaptured Baba Amr from its lightly armed defenders on Thursday after an almost month-long bombardment reduced much of the district to rubble.
The International Committee of the Red Cross and the Syrian Arab Red Crescent were still seeking approval from Syrian authorities to enter Baba Amr to help civilians there.
At the moment we are blocked by the Syrian army and government, Yves Daccord, the ICRC's director-general, told Swiss Radio and Television (RTS).
The situation is extremely difficult, the weather conditions are tragic. It is very cold, there is fighting and people don't have access to food or water, and above all there is a big problem of evacuating the wounded, he said.
ICRC and Syrian Red Crescent teams distributed food and blankets to civilians, including families who had fled Baba Amr, in two Homs neighbourhoods, ICRC spokesman Hicham Hassan said.
DESTRUCTION AND DEBRIS
Opposition activists have accused Syrian forces of carrying out bloody reprisals in Baba Amr, but their reports are hard to verify given Syria's severe curbs on independent media.
Human Rights Watch quoted local sources on Friday as saying about 700 civilians had been killed and thousands wounded in Homs since a military assault in the city began on February 3.
Secretly shot video footage aired by Britain's Channel 4 television shows what it said were Syrian patients being tortured by medical staff at a state-run hospital in Homs. The report could not be independently verified.
The state news agency SANA said the authorities had begun to remove destruction and debris left by armed terrorist groups in Inshaat and Baba Amr neighbourhoods in Homs on Sunday.
It said 16 members of the security forces killed by insurgents had been buried the same day.
The British-based Syrian Observatory for Human Rights said the security forces had killed eight people across Syria on Sunday and 29 the previous day. The Local Coordination Committees, a grassroots opposition group, put Sunday's death toll at 62.
Saudi Arabia and Qatar are among countries that have called for Syrian rebels to be armed, but there is little appetite in the West for Libya-style military intervention that could have unforeseen consequences in the conflict-prone Middle East.
(Additional reporting by Khaled Yacoub Oweis in Amman, Oliver Holmes in Arsal, Stephanie Nebehay in Geneva, Tim Hepher and John Irish in Paris, Robert Mueller in Prague, Alexei Anischuk in Moscow, Ayman Samir in Cairo, Chris Buckley in Beijing, David Ljunggren in Ottawa and Tim Castle and Estelle Shirbon in London; Writing by Alistair Lyon; Editing by Michael Roddy)