U.S. Secretary of State John Kerry says he refuses to get into a "back and forth" with Iran about whether U.S. officials asked Iran to help fight against Islamic State (IS) militants.
Iranian Supreme Leader Ayatollah Ali Khamenei said earlier on September 15 that Tehran had rejected a request by Washington to cooperate in the fight against the IS.
Khamenei said the request had been made by the U.S. ambassador in Iraq to Iran's envoy in Baghdad.
But Kerry, in Paris after meetings with officials from 25 other countries about IS insurgents, said arguing with Iran is not "constructive."
He added he has "no idea what interoperation [the Iranians] drew from any discussion that may or may not have taken place."
Kerry said over the weekend that Iran's attendance at the Paris conference would be inappropriate.