The Friends of Syria nations that support regime change meet in Morocco on Wednesday for the first time since the creation of a new opposition coalition seeking wider international recognition.
Arab and Western states will consider two key issues concerning the 21-month conflict -- the political transition in the event of President Bashar al-Assad's fall, and mobilising vital humanitarian aid as winter sets in.
Since the last meeting, in Paris in July, the number of people killed has risen from 16,000 to more than 42,000, the Britain-based Syrian Observatory for Human Rights says.
Wednesday's meeting will address ways of supporting the National Coalition, which "brings together a very broad range of opposition factions and individuals" and is a "very credible interlocutor," according to Rabat.
Under international pressure to unite, Syrian opponents of the Assad regime agreed in Doha on November 11 to establish the coalition and group the various rebel forces under a supreme military council.
The Gulf Cooperation Council, France, Britain and Turkey have all formally recognised the coalition as the sole legitimate representative of the Syrian people.
But it has failed to win universal backing amid doubts over whether it genuinely represents all sectors of Syrian society. Many are looking to see if it wins Washington's formal endorsement.
Comments by US officials have raised this prospect.
"Now that there is a new opposition formed, we are going to be doing what we can to support that opposition," US Secretary of State Hillary Clinton said in Brussels last week.
"This is a pretty nascent group, but they clearly seem to be moving in the right direction," said State Department spokesman Mark Toner.
In the latest move to bolster its credentials, the coalition plans to announce the creation of a military council before Wednesday's meeting, bringing most of the rebel groups under a single command structure.
Radical Islamist groups such as Al-Nusra Front will notably be excluded, amid US concerns that weapons supplied to the rebels have been reaching jihadist groups.
Other countries are pushing for international acceptance of the coalition as the Syrian people's legitimate representative.
"We hope that the maximum number of countries join our ranks, but I don't know if this recognition will take place individually or in groups," said a French foreign ministry spokesman.
"We hope that (the meeting) lays the foundations for the constitution of a provisional government in Syria," he added.
National Coalition chief Ahmed Moaz al-Khatib has expressed optimism about a positive outcome from Marrakesh, with more than 100 delegations due to attend.
"There are many countries, in Europe, the United States and the Gulf, that have shown great understanding," he told AFP.
He urged participants to ensure that the conference "remains true to its name," urging them to show "that they are real friends of Syria, by offering their support with all the resources possible."
Khatib also said humanitarian aid was a "priority."
Clinton touched on the same question last week during a NATO meeting, calling Assad's fall "inevitable" and saying it was "just a question of how many people will die until that date occurs."
Washington has provided around $200 million in humanitarian assistance, as well as non-lethal aid to the rebels, officially declining to send arms.
But it has warned of "consequences" should Damascus unleash chemical weapons on its own people, amid concerns over the possible use of deadly sarin gas.
"We are extremely concerned," British Foreign Secretary William Hague told reporters on Saturday.
He said London had joined Washington in delivering a strong message to Assad's government that if it uses chemical weapons the global community had "contingency plans," without specifying what they were.
Syria has insisted it would never countenance such a policy, suggesting instead that the rebels themselves may use chemical weapons.