Iran has refused an offer from the United States to join a global alliance preparing to combat Islamic State militants, according to Iran’s supreme leader, Ayatollah Ali Khamenei.

Khamenei said Monday that the US offered to discuss a coordinated effort with Iran against Islamic State (IS, also known as ISIS or ISIL), a common foe in the region, in the midst of an escalating campaign of violence that continues to claim lives across Iraq in Syria.