The "Friends of Syria" conference has concluded in Paris with unanimous agreement that Syrian President Bashar al-Assad "must go."
French Foreign Minister Laurent Fabius told reporters that representatives from over 100 countries and members of the Syrian opposition agreed that "Bashar al-Assad must go, and the sooner the better."
The United States, France, and Britain called for tougher sanctions against Damascus and slammed Russia and China for hampering efforts to end the conflict.
Russia and China boycotted the meeting.
U.S. Secretary of State Hillary Clinton called for a UN resolution on a political transition in Syria backed by sanctions against Assad and his inner circle.
She added that Russia and China needed to "pay a price" for blocking action against Assad, who has led a crackdown that's thought to have killed more than 16,000 people since unrest and insurrection broke out amid Arab Spring uprisings in early 2011.
British Secretary William Hague said countries that do not impose sanctions on Assad's government are effectively allowing killings to continue.
"It is no longer debatable that this crisis has become a threat to international peace and security," Hollande said. "So we must now draw the conclusions. Bashar al-Assad must go. A government of transition must be formed. This is in everyone's interests."
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Representatives from more than 100 countries and dozens of Syrian opposition figures were attending the conference.
Without naming them, Hollande warned Assad's backers that Syrian authorities were fostering chaos that would eventually threaten their own interests.
The French leader called for an increase in humanitarian aid to Syria and greater backing for its opposition, including providing rebels with communications equipment.
Hollande also urged the United Nations Security Council to take urgent measures to end the bloodshed.
"Today, our meeting here in Paris must set itself one goal: encourage the [UN] Security Council to take its responsibilities as soon as possible to better support the plan to end the crisis presented by special envoy Kofi Annan," Hollande said.
The fractured and frustrated Syrian opposition has chided the international community for moving too slowly.
The head of the opposition Syrian National Council, Hassan Hashimi, urged in Paris that a no-fly zone be introduced to prevent Assad's forces from targeting civilians and defecting soldiers.
The "Friends of Syria" meeting comes amid reports that a high-profile Syrian general and close ally of Assad has defected. Syrian Brigadier-General Manaf Tlas represents the highest-ranking military officer to have abandoned the Syrian regime.
The Syrian Observatory for Human Rights says more than 16,500 people have been killed in violence since the uprising against Assad's rule broke out in March last year.
Ahmed Ramadan and Mohamed Faruq Tayfur, both members of the executive committee of the anti-Assad Syrian National Council, said the international community needed to take "serious measures" to resolve the crisis in Syria.
Ramadan said the peace plan of international envoy Kofi Annan needed to be placed under Chapter 7.
''The international community feels now that it needs to take new measures after the Annan plan and what the regime did to undermine it, I think the Paris conference must recommend going to the Security Council and issuing a new resolution under Chapter 7 and there should be clear support for the Syrian National Council and the Free Army,'' Ramadan said.
Tayfur said if such steps aren't taken, the Annan plan "is finished."
''Concerning the Annan plan, if there were serious measures to implement it like under Chapter 7 or there were serious indications that the plan will be implemented, then we have no problem with it. But if there were no clear measures like this then it is useless, it is finished. Expired,'' Tayfur said.
Based on reporting by Reuters, dpa, and AFP