Ayatollah Ali Khamenei Holocaust Persian New Year Iran
Iran's Supreme Leader Ayatollah Ali Khamenei said he rejected US' offered because it had "corrupted its hands".Reuters

Iran has rejected a request from the United States to cooperate in action against the Sunni terror group Isis in Iraq and Syria, the country's supreme leader has revealed.

"Right from the start, the United States asked through its ambassador in Iraq whether we could cooperate against Daesh (Arabic acronym for ISIS)," Khamenei said in an official statement on his website.

"I said no, because they have dirty hands," said Khamenei, who has the final say on all matters of state in Iran.

"Secretary of State (John Kerry) personally asked (Iranian Foreign Minister) Mohammad Javad Zarif and he rejected the request," said Khamenei.

Khamenei tweeted: "I rejected US offer to Iran abt Isis because US has corrupted its hands in this issues. Mr. Zarif rejected US Secretary of State's offer too."

The Iranian rejection came as an international summit of foreign ministers convened in Paris to discuss a combined strategy to tackle the terror group.

Approximately 40 countries have joined a coalition to battle the militants in Iraq and Syria, who have beheaded two American journalists and one British aid worker in recent weeks.

Opening the summit, French President Francois Hollande spoke of support for Syrian moderate rebels.

"Chaos plays into the terrorists' hands," he said.

"Therefore we have to support those who are able to negotiate and make the necessary compromise in order to preserve the future of Syria, and for France those are the forces of the democratic opposition."

Ten Arab states have joined the international coalition. They are: Egypt, Iraq, Jordan, Lebanon, Bahrain, Kuwait, Oman, Qatar, Saudi Arabia, and the United Arab Emirates (UAE).