Syria will retaliate against any country that recognises the opposition National Council, Foreign Minister Walid Muallem said on Sunday.
"We will take significant measures against any country that recognises this illegimate council," Muallem told a news conference, as the newly formed opposition group lobbied for support in Cairo.
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Formed in Istanbul at the end of August, the Syrian National Council unites all the major known factions opposing Assad's rule, both inside and outside Syria.
It includes the Local Coordination Committees, an activist network spurring protests in Syria, the long-banned Muslim Brotherhood as well as Kurdish and Assyrian groups.
The United Nations estimates that a total of more than 2,900 people have been killed since Syria launched its brutal crackdown on dissent in mid-March.
But Damascus plays down the scope of the opposition movement and blames "terrorists" and "armed gangs" for the country's violence.