The United States and "wicked" Britain are responsible for the creation of the Islamic State (formerly known as Isis,) according to Iran's supreme leader Ayatollah Ali Khamenei.
In his first public intervention since undergoing prostate surgery last month, Khamenei, 75, delivered a hardline speech for the Shi'ite Muslim religious holiday of Eid al-Ghadeer blaming "America, Zionism and especially the veteran expert of spreading divisions - the wicked government of Britain" for creating divisions between Sunnis and Shi'ites that led to the spread of Islamic State (IS).
"They created Al Qaeda and Da'esh in order to create divisions and to fight against the Islamic Republic, but today, they have turned on them [Islamic State]," Khamenei said.
On 23 September, a US-led coalition including Sunni Arab monarchies of the Gulf started a campaign of air strikes in an attempt to crush a radical Sunni Islamist insurgency that conquered vast swathes of land between Iraq and Syria.
Iran and the US both oppose IS fighters but have failed so far to find common ground for a joint effort against the jihadists. The Islamic Republic is a longstanding ally of the Assad regime in Syria. Bashar al-Assad is a member of the Alawite sect, an offshoot of Shi'ite Islam.
Khamenei also accused the US and Britain of using the Islamist threat to justify their presence in the Middle East.
"A careful and analytic look at the developments reveals that the US and its allies, in efforts that are falsely termed countering Da'esh, seek to create division and enmity among the Muslims rather to destroy the root causes of that [terrorist] current," Khamenei said.
"Shi'ites and Sunnis must know that any action or remark, including insulting one another, leads to increased sensitivities and ignites flames. This will certainly benefit the common enemy of all Muslims."
The development came as Turkey denied allowing the US to use its Incirlik base for operations against Islamic State but said talks are continuing on the subject.