A group of 11 Western states and Arab powers - including three permanent members of the UN Security Council - today agreed to put their "united and collective weight" behind pressure for a United Nations-led peace process in Syria.
The Friends of Syria group, meeting in London, called on both sides in the two-and-a-half year civil war to participate in the planned "Geneva II" talks to forge a transitional government for the Middle Eastern state.
The group agreed to continue to provide "intensive political and practical support" to the Syrian National Coalition, an umbrella group for moderate armed forces seeking the overthrow of President Bashar Assad, said Foreign Secretary William Hague, who hosted the meeting at the Foreign Office.
Mr Hague said that, before the talks open in Switzerland, the UK will announce a further package of support for the SNC, whose president Ahmed Jarba attended today's gathering along with US Secretary of State John Kerry and ministers from France, Germany, Italy, Qatar, Saudi Arabia, Turkey, Jordan, the United Arab Emirates and Egypt.
British support will include "substantial" non-lethal supplies such as communications, medical and logistical equipment, said the Foreign Secretary.
"There can be no peaceful and political solution in Syria without the participation of a moderate opposition," said Mr Hague. "We pledged our further support to them."
And he added: "It is important that we don't abandon them, we keep faith with them.
"Through the Geneva II process, we will be with them every step of the way, giving them the support they need as well as the practical and administrative support needed to carry out such a negotiation."
Mr Hague said that the Friends of Syria were not making it a precondition of the Geneva talks that Assad can have no part in the political future of his country, but he made clear that he does not expect there to be a place for him in any transitional administration.
Speaking at the end of today's meeting, Mr Hague said: "The only sustainable way to end this conflict and the suffering of Syrian civilians is through a political transition.
"The purpose of our meeting today has been to send a signal of our resolve, our unity and our determination in bringing that about."
The Friends of Syria group agreed to "put our united and collective weight behind the UN-led Geneva II process which must lead to establishing by mutual consent a transitional governing body with full executive powers", as set out following earlier talks in the Swiss city in June 2012, said the Foreign Secretary.
"By definition, mutual consent means it can only be agreed with the assent of the SNC, so Assad would play no role in that future government of Syria," he added.
The group also urged the SNC to "commit itself fully to the Geneva II process and to lead and form the heart of any opposition delegation".
Mr Hague said: "Geneva offers the Syrian people the best hope to improve their lives.
"We agreed that we will provide the intensive political and practical support that will be required to give the Geneva II process the best chance of success."
Mr Hague said that the Assad regime was continuing to use "disproportionate force" in response to the uprising, much of it directed at civilians.
The regime was "laying siege to desperate people and presiding over a humanitarian catastrophe, with people under siege and people starving", he said.
He warned of a "deepening humanitarian disaster" and called on the regime to allow "full and uninhibited access to people in humanitarian need".
He acknowledged that the Geneva II process faced "immense difficulties", but warned that unless moderate forces were supported, the country would be left at the mercy of either Assad or extremist jihadists who have latched onto the conflict.
"The alternative (to Geneva II) is a protracted conflict in which neither side will be able to achieve a military victory over the other," said Mr Hague.