The United States is pushing for the formation of a broad international coalition to tackle IS which has captured swathes of Iraq and Syria, and has already secured the backing of 10 Arab states including Saudi Arabia.
"The role of (the) international coalition against terrorism should be very clear," Hadi el-Bahra, head of the Syrian National Coalition, said at a news conference in Abu Dhabi.
The SNC gathers together various groups seeking the overthrow of Syrian President Bashar al-Assad but has been weakened by divisions despite the support of Western countries and Saudi Arabia.
Bahra said the SNC was "100 per cent" capable of fighting the IS "with a proper plan which we have put in place and which we ask the international community to support".
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The group would launch two offensives at the same time, "one against the regime and one against IS", Bahra said.
US President Barack Obama said on Wednesday he had authorised the expansion to Syria of the US air campaign against IS he launched in Iraq in early August.