Russian President Vladimir Putin has called for a regional "co-ordinating structure" against Islamic State.
Putin reiterated his support for Syrian President Bashar al-Assad, who Western countries and the Syrian opposition have said must go.
The crisis is expected to be high on the agenda as world leaders gather at the UN in New York.
UK Prime Minister David Cameron is expected to soften his stance against Assad in a speech this week.
He is expected to tell the annual meeting of the UN General Assembly in New York that Assad could remain temporarily in power at the head of a transitional government.