France has become the first Western power to recognise the newly united Syrian opposition as the only representative of the Syrian people.
"France recognises the Syrian National Coalition as the only representative of the Syrian people and therefore as the future provisional government of a democratic Syria," President Francois Hollande told a press conference in Paris on Tuesday.
The question of arming the rebels would be looked at as soon as the rebel coalition formed a transitional government, Hollande said.
The announcement comes after opposition groups agreed on Sunday in Doha to unite against the government of President Bashar al-Assad.
On Wednesday, Faisal Muqdad, Syria's deputy foreign minister, called the Doha meeting a "declaration of war."
"These people [the opposition] don't want to solve the issue peacefully through the mechanisms of the UN," Muqdad told AFP.
"We read the Doha document and they reject any dialogue with the government,” Muqdad said.
The United States said on Tuesday that the coalition was "a legitimate representative" of the Syrian people, but stopped short of recognising it as the sole representative.
"We have long called for this kind of organisation. We want to see that momentum maintained," said US Secretary of State Hillary Clinton, during a visit to the Australian city of Perth.
"As the Syrian opposition takes these steps and demonstrates its effectiveness in advancing the cause of a unified, democratic, pluralistic Syria, we will be prepared to work with them to deliver assistance to the Syrian people."
Arab League and European Union foreign ministers pledged after their meeting in Cairo on Tuesday to support the Syrian opposition and welcomed steps to unite the various groups under a new, united banner, in order to facilitate a solution to the 20-month conflict.
"The ministers welcomed the formation of the Syrian National Coalition for Opposition and Revolutionary Forces. They called on all opposition groups to adhere to the national coalition and on the national coalition to engage with all sections of Syrian society," said a statement issued at the close of the meeting held in Cairo on Tuesday.
Syria's divided opposition had come under pressure from Western powers to join forces and offer a single interlocutor during negotiations, in order to provide a single contact for international critics of the regime's efforts to stamp down the opposition since 2011.
The coalition brings together the Syrian National Council and other groups inside Syria.
The Arab League has recognised the coalition as "the legitimate representative of the Syrian people's aspirations."
Secretary General Nabil al-Arabi described it as "a glimmer of hope."
Frustration at UN deadlock
British Foreign Secretary William Hague called on the group "to demonstrate they are acting on behalf of all Syria's communities. The more progress the coalition makes towards those goals, the greater practical support it will have from the United Kingdom."
Hague expressed frustration at the deadlock on Syria in the UN Security Council, saying that "our efforts ... to encourage the UNSC to take on its responsibilities have been vetoed by Russia and China. In the absence of such progress, we will increase our support to Syrian opposition groups."
Russian Prime Minister Dmitry Medvedev criticised countries siding with the opposition and insisted Moscow was staying neutral.
"We don't support anybody in this conflict, neither President Assad nor the rebels ... but unfortunately, the point of view of some states is more one-sided," Medvedev told Finnish newspaper Helsingin Sanomat.
Moscow and Beijing, both allies of President Assad, have vetoed three Western-and Arab-backed resolutions at the Security Council condemning the Syrian regime for violence.
German Foreign Minister Guido Westerwelle said his country "is ready to join hands with the Arab League to help (the new alliance) to become a credible and inclusive alternative to al-Assad's regime."
Westerwelle and French Foreign Minister Laurent Fabius both met the head of the coalition, Mouaz al-Khatib.