The United States and Iran have denied plans for any military coordination in the fight against Islamic State militants operating in Iraq and Syria.
"We are not going to coordinate military action or share intelligence with Iran and have no plans to do so," State Department deputy spokeswoman Marie Harf said Friday, reacting to reports that Tehran had approved such an arrangement.
Harf said that Washington was "open to engaging" with Iran as it had in the past on select issues, notably on Afghanistan in late 2001, when the two sides worked to put Hamid Karzai into power after the fall of the Taliban.
"But we will not be coordinating our action together," she added.
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The BBC reported, citing unnamed sources in Tehran, that Iran's supreme leader Ayatollah Ali Khamenei had approved cooperation with the US in the fight against the Islamic State.
In a brief statement on Iranian state media, foreign ministry spokeswoman Marzieh Afkham denied the report.
"Iran's stance has already been declared and this news is not correct," she added.
US and Iranian officials met earlier for a second day in Geneva as they work toward hammering out a full deal on Tehran's controversial nuclear program ahead of a November deadline.
The two countries have not had diplomatic relations in more than 30 years, but in the past year have seen a bit of a rapprochement as they work on the nuclear deal.