President Barack Obama has said the US now considers Syria's main opposition group the sole "legitimate representative" of the country's people, deeming the move "a big step" in the international diplomatic efforts to end President Bashar al-Assad's rule.
Obama said the newly formed Syrian National Coalition "is now inclusive enough" to be granted the elevated status.
"Obviously, with that recognition comes responsibilities," Obama said in an interview on Tuesday with American ABC News. "To make sure that they organise themselves effectively, that they are representative of all the parties, that they commit themselves to a political transition that respects women's rights and minority rights."
The move, which was widely expected, could give new international legitimacy to the rebels fighting to overthrow Assad, but stops short of authorising US arming of the opposition.
Washington has so far only provided humanitarian, non-lethal aid to the rebels, officially declining to send arms, a position White House spokesman Jay Carney reiterated on Tuesday.
Recognition of the council as the sole representative of Syria's population brings the US in line with Britain, France, Turkey and the Gulf Cooperation Council, which took the same step shortly after the body was created at a meeting of opposition representatives in Qatar last month.
European foreign ministers met the coalition's leader, Ahmed Mouaz al-Khatib, in Brussels on Monday and said in a statement that the EU accepts the bloc as "legitimate representatives of the Syrian people".
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The Friends of Syria group, an international collective of countries meeting periodically, are set to meet in the Moroccan city of Marrakesh on Wednesday.
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The group does not include Russia and China, which have blocked unified international action on Syria at UN Security Council level.
Obama's announcement follows his administration's blacklisting earlier on Tuesday of a Syrian rebel group, the al-Nusra front, saying it was trying to hijack the uprising on behalf of al-Qaeda in Iraq.
Andrew Tabler, a Syria expert at the Washington Institute for Near East Policy, said it was "far from clear" what the US recognition of the coalition would give the opposition.
"It's designed to give them a political shot in the arm," he said. "But the fact that this announcement comes after the US designated Jabat al-Nusra as a terrorist organisation has indicated to many in the Syrian opposition that the United States is more concerned about combating terrorism than it is with supporting the Syrian opposition.
"It's been a controversial move, and we have to wait and see what the formal announcement is tomorrow in Marrakesh."
The Syrian conflict started in March last year as an uprising against the regime of Assad, whose family has ruled the country for four decades. It gradually turned into a civil war, with rebels taking up arms to fight back against a bloody crackdown by the government. According to opposition activists, at least 40,000 people have been killed.