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Syria's main opposition group in exile says there can be no role for President Bashar Assad in any future transitional government.

In a statement, the Western-backed Syrian National Coalition also urges the international community to "prove its seriousness" ahead of a planned peace conference by securing humanitarian corridors so that aid can reach besieged areas of the country.

Tuesday's statement follows a United Nations announcement that the warring sides in Syria would attend a conference in Geneva on Jan. 22 — the first face-to-face talks to end the Syrian civil war.

Huge gaps remain however, particularly when it comes to Assad's future role. The coalition said the world must pressure Assad to allow aid to reach rebel-held areas ahead of the talks.