Kofi Annan's plan to resolve the Syrian crisis is "the last hope" for a country ravaged by a year-long crackdown on civilians, according to draft document issued by Friends of Syria coalition.

The 14-nation group met in Paris to discuss solutions and to put pressure on Syria's embattled President Bashar al-Assad to end violence.

The country could plunge into a civil war if the plan elaborated by UN envoy Kofi Annan fails, the statement warned.

""Though fragile, the Annan mission represents a last hope."

US Secretary of State Hillary Clinton said the UN Security Council should reinforce sanctions against Syria along with adopting an arms embargo.

"We need to continue to work and move towards a Security Council authorisation so that we have the authority to proceed when the times are right," she said.

"We need to start moving very vigorously in the Security Council for a Chapter 7 sanctions resolution, including travel, financial sanctions, an arms embargo, and the pressure that that will give us on the regime to push for compliance with Kofi Annan's six-point plan," she said.

Meanwhile, US military leaders confirmed there would be no unilateral military action in Syria, and diplomatic efforts remain the primary path to solve the crisis.

"There is no silver bullet," US Defence Secretary Leon Panetta said. "We also know that the complex problems in Syria cannot all be solved through the unilateral actions of the United States, or any other country. They demand a coordinated international response that is uniquely tailored to the situation".

He also revealed that the Pentagon has plans for establishing humanitarian corridors in the country, as suggested by French president Nicholas Sarkozy.

UN secretary general Ban Ki-moon said Syria was not honouring a UN-backed ceasefire.

Despite a decrease in violence, government troop attacks on rebel strongholds are still going on with casualties being reported on a daily basis.

The UK-based Syrian Observatory for Human Rights said explosions could be heard in the town of Qusair, near the border with Lebanon.

The international community and the United Nations still hope the monitoring teams will be able to stabilise the situation and push for greater observance of the peace plan.

But observers remain sceptical because of Assad's repeated broken promises to end the violence and previous UN monitoring teams' failure to stop the bloodshed.