The collapse of a deal between Syria's two main opposition factions shows that voices calling for foreign intervention to topple President Bashar al-Assad have gained the upper hand over those rejecting it.

But the quick unravelling of the pact, which ruled out such international action, ensures that achieving that goal will remain elusive since Western powers are loath to throw their weight behind a fractured Syrian opposition.

Wary of the risks of engendering chaos and wider Middle East conflict given Syria's internal sectarian divisions and Assad's alliance with Iran, NATO says it has no plans to intervene as it did to back Libyan rebels who toppled Muammar Gaddafi last year.

And neighbouring Turkey, Assad's former ally, has said any intervention must be backed by the U.N. Security Council with Arab League support, must be justified on humanitarian grounds and not have regime change as its goal.

Ten days ago Burhan Ghalioun, head of the mostly exiled Syrian National Council (SNC), signed an accord with the mainly Syrian-based National Coordination Body (NCB) outlining a transition to a democratic post-Assad Syria.

The agreement rejected any military intervention that harms the sovereignty or stability of the country, while leaving the door open for an Arab role to stop Assad's military crackdown on protests in which 5,000 people have died, by a U.N. count.

But members of Ghalioun's own council denounced the deal, forcing him to disavow it. Many grassroots protesters inside Syria also rejected it, saying they had lost hope that 10 months of peaceful demonstrations - now accompanied by an armed insurgency in some regions - would bring down Assad.

The paper has been cancelled after pressure from members of the council. Some threatened to resign, said SNC member Khaled Kamal. Ghalioun signed it without the knowledge of council members, so after consultation he withdrew his signature.

SNC members were holding a meeting in Turkey on Monday to draft their own road map for change and were expected to decide whether to replace Ghalioun as council chief.

The NCB rejects foreign intervention, seeking instead a political agreement for a transitional government to replace Assad, a path it says would save Syria from disintegrating along sectarian and ethnic lines.

Kamal said many SNC members had originally shared the NCB's rejection of an intervention such as a no-fly zone or buffer zone to protect Syrian civilians. But now all roads are blocked and the political solution did not work, he said.

After ten months and after we knocked on all doors... foreign intervention is the only choice before us, he said, adding that the SNC will begin a campaign to get recognition as the only opposition group representing the mass demonstrations.

COUNCIL SEEKS FOREIGN ROLE

The protests, driven by anger and frustration at corruption, poverty and lack of freedoms over 41 years of autocratic Assad family rule, have been mainly peaceful, though rights groups say the death toll among protesters now exceeds 5,000.

The revolt has become bloodier as protests have become overshadowed by armed rebels taking the fight to the security forces. Syria says it is fighting Islamist militants who it blames for killing 2,000 of its security forces and soldiers.

The National Council, ignoring Ghalioun's concerns of possible civil war, wants to give a bigger role for the rebel Free Syrian Army that has been attacking security forces.

It is also seeking international steps to prevent Assad using warplanes against popular unrest and to create a buffer zone on the Turkish border, which would provide the FSA a base to escalate attacks on Assad's forces.

Such views are echoed among many activists in flashpoint cities such as Homs and Hama who say Arab League monitors assessing whether Damascus is complying with a plan to end violence are toothless and will not protect civilians.

The best thing they can do for us is to refer Syria to the (U.N.) Security Council, said an activist called Ahmad.

SNC leaders meeting in Istanbul re-elected Ghalioun on Monday for one month as head of the group, an opposition source said, pending the creation of a better mechanism to choose a leader.

Khalaf Dahowd, a member of the executive bureau of the National Coordination Body, said he had no sense during meetings held with foreign officials that the international community was ready to step in.

Syria has strong allies. The Russians told us we will not use one veto - we will use 20 vetoes in the Security Council, he said. Assad is backed by Iran and the powerful Shi'ite Muslim Lebanese militant group Hezbollah. He also has allies in Russia and China, which have blocked Western-generated draft resolutions against Damascus at the U.N. Security Council.

We are against the militarisation of the revolution because it justifies the oppression and the use of force. Tens of people are getting killed now but if the revolution becomes a military one then hundreds will be killed, Dahowd said.

Syria is a country of many sects and ethnicities. Foreign intervention will break the social infrastructure of Syria and its political borders, he said.

Already many analysts and officials have warned that the increasingly lethal armed confrontations could tip Syria into a sectarian civil war, pitting majority Sunni Muslims against Assad's minority Alawite sect, an offshoot of Shi'ite Islam.

RIFTS, MISTRUST EXPOSED

Years of oppression under Assad's late father, Hafez al-Assad, have fragmented a Syrian opposition that includes liberals, Arab nationalists, Islamists and Kurds.

The Islamist Muslim Brotherhood, whose armed revolt was crushed with up to 30,000 deaths by the elder Assad in the city of Hama in 1982, is believed to be a major force among those in the Sunni majority keen to throw off domination by Alawites.

Over the years Syria's intelligence agents have worked tirelessly to divide the various opposition groups, playing on their rivalries to plant seeds of doubt among them and leaving a legacy of suspicion still evident in their responses to a grassroots uprising which they played little role in creating.

Many of the members of the Coordination Body are agents of the Syrian regime and some are scared of the regime because many of them are inside Syria, said Kamal of the National Council.

Privately other opposition figures level similar accusations against the SNC, saying it is riddled with agents of Assad.

An opposition source familiar with talks held with Western officials said that the officials spelled out to each group they met that the Syrian opposition should unite and that none of the groups could claim to be the main opposition movement.

A Syrian opposition figure in Damascus who refused to be named said: There is opposition inside Syria that nobody should ignore. The (National) Council is not the only representative of the opposition.

Even if they rejected the deal at the end of the day the opposition has no alternative (but) to sit down and talk. They must agree. The Council is crazy to think the United Nations is going to recognise them now, he said.

(Editing by Dominic Evans and Mark Heinrich)