Foreign minister tells conference on Syria that supplying weapons to rebels fighting Assad regime is 'an excellent idea' as Obama vows to use 'every tool available' to stop the slaughter.
Saudi Arabia has backed the arming of Syria's opposition guerrilla army in remarks that could signal an intervention by the Sunni Muslim superpower in the Assad regime's crackdown against the uprising.
The Saudi foreign minister, Prince Saud al-Faisal, described the arming of the Free Syria Army as an "excellent idea" at an inaugural meeting in Tunisia of an anti-Assad group – the Friends of Syria.
But the Saudi delegation later walked out of the summit citing "inactivity" among the member states gathered.
Qatar's foreign minister, Sheikh Hamad bin Jassim al-Thani, called for the creation of an Arab force to "open humanitarian corridors to provide security to the Syrian people".
In the Syrian city of Homs, the International Committee of the Red Cross (ICRC) said it had begun to evacuate women and children from the Baba Amr district, where injured western journalists including the Le Figaro reporter Edith Bouvier and the Sunday Times photographer Paul Conroy had become stranded.
The ICRC said 27 Syrian women and children had been taken to a hospital elsewhere in the city. "It's a first step forward," ICRC chief spokeswoman Carla Haddad told Reuters in Geneva. "The priority now is evacuating the seriously wounded or sick." She said the injured journalists were not among those evacuated.
The first day of the three-day summit in Tunis offered little to stem the rapidly deteriorating situation, although Russia, a key ally of Syria, added its voice to calls for a ceasefire to allow aid to reach areas in desperate need, such as Homs. Hopes for a ceasefire had been the centrepiece of the summit, which is being attended by almost 80 countries, many of whom are looking for ways to embolden Syria's opposition movement.
In Baba Amr, where 20,000 residents remain under military siege, neither the west nor the opposition Syrian National Council are seen as saviours. "Nothing has changed it is the same situation, the same siege," one resident told the Guardian. "They keep killing and nobody cares about our lives. We feel a lot of anger.
"Is there any real action from the world? We don't want statements. He [President Bashar al-Assad] will never stop. He will keep killing. We want them to protect our families, our children, our women. To provide food, to provide medicine. To remove this dictatorship from our head.
"Any kind of protection for civilians would be welcome. Military [intervention] would be welcome. We want action to stop the bloodshed. We want them to remove Bashar al-Assad."
In Washington President Barack Obama said the US and its allies would use "every tool available" to stop the slaughter of innocent people in Syria, uttering his most forceful words to date in response to an increasingly grim crisis that has gripped the world.
"It is absolutely imperative for the international community to rally and send a clear message to President Assad that it is time for a transition," Obama said.
"It is time for that regime to move on. And it is time to stop the killing of Syrian citizens by their own government."
He added that nations cannot afford to be "bystanders" as the killing continues.
Britain has formally recognised the SNC as a legitimate representative of the Syrian people in a move it hopes will propel the disjointed opposition and generate a global shift away from Assad's regime.
The foreign secretary William Hague's announcement in Tunis marks the first time a western state has given full backing to the nascent opposition, which had failed to lock in patrons despite a brazen and ferocious year-long regime assault on dissent.
He called on leaders of the 80 states represented in Tunis to "tighten the diplomatic and economic stranglehold" on the Syrian government, whose leaders have been already been hit with a series of increasingly harsh sanctions.
"We, in common with other nations, will now treat them and recognise them as a legitimate representative of the Syrian people," Hague said.
At the same time, the US, France and other western countries are pushing Assad to agree to a ceasefire, particularly in Homs, which was on Friday again pounded by rockets and shells for a 21st consecutive day.
Hillary Clinton warned Assad would pay a heavy price for the violence in Syria and said he must allow in urgent humanitarian relief. "If the Assad regime refuses to allow this life-saving aid to reach civilians, it will have even more blood on its hands," said the US secretary of state. "So too will those nations that continue to protect and arm the regime."
She appealed to Syrian security forces to disobey orders from their commanders to carry out acts of violence. "Their refusal to continue this slaughter will make them heroes in the eyes of not only Syrians but people of conscience everywhere. They can help the guns fall silent."
In Gaza , leaders of the Palestinian Islamist movement Hamas publicly endorsed the opposition movement in Syria, depriving Assad of one of his few remaining Sunni Muslim supporters in the Arab world, deepening his international isolation.
The SNC has signalled it will drop its objection to arm the opposition Free Syria Army, which is battling loyalist military. The SNC has suggested it would no longer oppose foreign military trainers, advisers, or even weapons, if the regime failed to agree to the terms of an Arab League initiative to end the violence.
"If the regime fails to accept the terms of the political initiative outlined by the Arab League and end violence against citizens, the Friends of Syria should not constrain individual countries from aiding the Syrian opposition by means of military advisers, training and provision of arms to defend themselves," the SNC said.
The key plank of the Arab League plan was a call for Assad to stand down, something which he, along with his allies, Russia, China and Iran, have rejected.
Instead, he is pushing ahead with a referendum on a new constitution, scheduled for Sunday, which aims to reorientate the totalitarian state towards a more pluralistic political system.
The Friends of Syria conference marks the best opportunity yet for the political opposition to shake off the same misgivings and win the confidence of the west, which has waited a year before choosing to embrace it. The SNC represents only around 70% of Syria's opposition movement and had so far struggled to adopt unified stances on many key issues.
• This article was amended on 25 February 2012. It mistakenly stated that Britain had severed ties with Damascus. This has been corrected.