PARIS: US Secretary of State Hillary Clinton urged the UN to use the threat of sanctions to force change in Syria Friday as President Bashar al-Assad was rocked by the defection of one of his most senior generals.

Speaking at a Friends of Syria meeting in Paris, the top US diplomat also rounded on Russia and China, telling delegates from over 100 countries gathered in the French capital that the pair were blocking progress towards peace.

French President Francois Hollande also pushed for the United Nations Security Council to get tough with Damascus, while the Syrian opposition called for humanitarian corridors and a no-fly zone to be implemented.

A peace plan drawn up by former UN chief Kofi Annan, which insists on a cessation of violence by all sides, has made little headway and activists say an estimated 16,500 people have now died in the 16-month uprising.

A meeting last weekend of world powers in Geneva agreed to a transition plan that the Syria opposition, the West and Russia have interpreted differently, but Clinton insisted the plan amounted to a call for Assad to go.

“It is imperative to go back to the Security Council and demand implementation of Kofi Annan's plan including the Geneva communique that Russia and China have already agreed to,” Clinton said.

“We should go back and ask for a resolution in the Security Council that imposes real and immediate consequences for non-compliance, including sanctions,” ranging from economic measures to military force, she added.

China backed Russia at the Geneva talks, insisting Syrians must decide how the transition should occur, rather than allowing others to dictate their fate.

The West insists Assad should not be part of any new unity government and the Syrian opposition rejected the Geneva talks as making concessions to Damascus under pressure from Russia.

Taking a tough tone, Clinton said she thought Russia and China did “not believe they are paying any price at all for standing up on behalf of the regime. The only way that will change is if every nation represented here directly and urgently makes it clear, that Russia and China will pay a price. They are holding up progress, blockading it. That is no longer tolerable,” Clinton said.

French President Francois Hollande said the uprising is now a threat to international security, echoing US calls for a tough UN resolution.

“To those who maintain also that Bashar al-Assad's regime, as dislikeable as it is, can avoid chaos, I tell them that they will have both the most dislikeable regime and chaos. And this chaos will threaten their interests,” Hollande said.

Russia, whose only Mediterranean naval port is in Syria, has twice blocked UN Security Council action on the Syrian conflict.

Although Moscow did not attend the meeting, a diplomatic source insisted that “Russian political and security circles are changing their position”.

“They agree that the situation is deteriorating... even if they continue to defend Moscow's policies,” the diplomat said on condition of anonymity.

China did not attend either of those meetings in which the United States, France, Britain, Germany as well as Saudi Arabia and Qatar led a group of more than 60 members, including most EU states and many Arab League nations.

Assad's regime was dealt another blow when it emerged on Friday that General Munaf Tlass, the son of a former defence minister who was a close friend of Assad's late father and predecessor, Hafez, had defected.

Tlass, a member of the inner circle of power in Syria, and a childhood friend of Assad, is the highest-ranking military officer to have abandoned the Syrian regime.

A source in Damascus told AFP that Tlass' relations with the authorities became irreconcilable after the regime's fierce assault on the Homs district of Baba Amr in February.

Tlass reportedly refused to lead the unit tasked with reclaiming Baba Amr, and Assad subsequently told him to stay at home.

Sources close to Tlass say his family is now in Dubai while French Foreign Minister Laurent Fabius said he would soon head to Paris.

The defection represents a major coup for the Surian opposition, some of whose leaders were in Paris for the conference.

The head of the main opposition group, the Syrian National Council, said in a speech at the meeting that humanitarian corridors and a no-fly zone should be implemented.

“All steps have to be taken to establish humanitarian corridors and a no-fly zone,” Abdel Basset Sayda said, claiming that Assad's regime “is about to fall.”Arab League Secretary General Nabil al-Arabi called on the Paris meeting to stop the escalating bloodshed in Syria.

“This conference must show clear, effective support. A simple declaration of intent is not enough. We need to force the Security Council to adopt a resolution to put an end to this tragedy.”