The Gulf Co-operation Council (GCC) has said its six member states decided to recognise the newly formed National Coalition of the Syrian opposition as the "legitimate representative" of the Syrian people.
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The GCC's move came a year after the Arab League suspended Syria's membership, and as the National Coalition met Arab foreign ministers in Cairo on Monday, buoyed by the hard-won unity deal.
The Arab League also recognised the newly formed Syrian opposition bloc's role, urging more opposition groups to join the coalition. But their official phrasing was reportedly not as strong as the wording used by the GCC.
"The states of the council announce recognising the National Coalition for the Forces of the Syrian Revolution and Opposition ... as the legitimate representative of the brotherly Syrian people," GCC chief Abdullatif al-Zayani
said in a statement on Monday.
The oil-rich bloc, which comprises Saudi Arabia, Bahrain, the United Arab Emirates, Oman, Qatar and Kuwait, would support the coalition "in order to achieve the aspirations of the Syrian people in hope that this will be a step towards a quick political transfer of power," Zayani said.
He hoped its formation would lead to ending the bloodshed and "a general national congress to pave the way to build a state ruled by law and open to all its citizens".
Al Jazeera's Jacky Rowland, reporting from Cairo, said, "The newly established coalition is now starting to get the recognition it needs from other bodies."
"But the Arab League stopped short of recognising it as the sole representative of the Syrian people," our correspondent said. "Rather it recognised the coalition [as representing] the 'aspirations' of the Syrian people."
"The coalition was given observer status [at the Arab League]. They haven't yet been offered the chair left empty since Assad was no longer welcome. So observer status is a good first step."
Hamad bin Jassim Al Thani, the Qatari prime minister whose government hosted the four-day talks that culminated in Sunday's unity deal, had said earlier that he would seek "full recognition" of the coalition.
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His minister of state for foreign affairs, Khaled al-Attiya, said recognition would remove any obstacles to the opposition securing arms for rebel fighters.
The National Coalition's newly installed leader, Mouaz al-Khatib, told Al Jazeera it already had promises of weapons, but did not say from whom.
Under Sunday's deal, the opposition agreed to establish a new supreme military council to take overall command of rebel groups on the ground - and address US concerns that weapons have been reaching hardline groups that are threatening to hijack the uprising.
Washington swiftly declared its backing for the new structure.
"We look forward to supporting the National Coalition as it charts a course toward the end of Assad's bloody rule and the start of the peaceful, just, democratic future that all the people of Syria deserve," State Department spokesman Mark Toner said.
Traditional Damascus ally Moscow, however, gave a cooler response, saying "such alliances must act based on a platform of peaceful regulation of the conflict by Syrians themselves, without interference."
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Britain hailed the agreement as an "important milestone in forming a broad and representative opposition that reflects the full diversity of the Syrian people".
Syria's former colonial ruler France said it would extend "full support to this coalition, in order for it to become a credible alternative" to Assad's regime.
The National Coalition also appointed two deputy leaders: prominent dissident Riad Seif, who was the architect of the new opposition structure; and secular female opposition figure Suhair al-Atassi, who hails from the central city of Homs, one of the bastions of the uprising.
A third post was left vacant for a representative of Syria's Kurdish minority.
As the opposition unveiled its new leadership, there was no let-up in the fighting on the ground. A total of 104 people were killed on Sunday, bringing to more than 37,000 number killed since March last year, the Syrian Observatory for Human Rights said.