The Syrian government says it will help the US fight Islamic State militants, who have seized huge swathes of land across Syria and Iraq.
Foreign Minister Walid Muallem said Syria was "the centre of the international coalition to fight Islamic State", adding that the US must coordinate with Syria before launching attacks in its territory.
"Anything outside this is considered aggression," he said.
The US has conducted air strikes on IS positions in Iraq, helping Kurdish forces to reclaim areas captured by the militants, and several countries, including France and Germany have announced that they will arm the Kurds.
British Foreign Secretary Phillip Hammond last week said the UK will not enter into a “poisonous” alliance with Syria, in order to fight IS.
Britain appoints security envoy to Kurdish regions in Iraq (24 August 2014)