US Secretary of State John Kerry raised the threat of Islamic militants in Iraq and Syria directly with his Iranian counterpart in high-level talks in New York, a US official said.
Kerry on Sunday met Iranian Foreign Minister Mohammad Javad Zarif for more than an hour at a hotel, during which they discussed progress in nuclear negotiations and "also discussed the threat posed by ISIL," a senior State Department official said, referring to the Islamic State group.
The top US diplomat has said Iran -- normally seen as Washington's arch-foe -- has a role to play as the United States seeks to build a coalition to combat the jihadists, who have seized control of a piece of Iraq and Syria.
Kerry also discussed his coalition-building efforts with his Russian counterpart Sergei Lavrov in a Sunday phone call.
Iran's supreme leader Ayatollah Ali Khamenei said last week that his government had rejected a request from the United States to join the coalition.
Iran and the United States do not have official diplomatic relations, and US officials have not confirmed or denied making such an offer in private.
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Washington has however publicly ruled out any military cooperation with Tehran, which it accuses of propping up the regime of Syrian President Bashar al-Assad and of being a state sponsor of global terrorism.
Zarif and Kerry met one-on-one first, before being joined by US Deputy Secretary Bill Burns and Under Secretary Wendy Sherman on the US side and Zarif's deputies Abbas Araqchi and Majid Takht-Ravanchi on the Iranian side, the State Department official said.
"They spent time reviewing the status of the EU-led P5+1 negotiations on Iran's nuclear program," the official added, referring to the nuclear talks being led by the five permanent members of the UN Security Council plus Germany.
"They discussed both the progress that has been made and the work that still needs to be done."
Kerry also talked with his Russian counterpart Lavrov "about how to broaden the conversation we've started on whatever role Russia may choose to play in the ISIL coalition," a second State Department official told reporters.
The official refused to be drawn further however on what role Moscow could take.
"We've been pretty clear about the menu of ways to contribute... so I think we're looking to hear from the Russians what their intentions are."
Lavrov and Kerry are due to meet in New York later in the week on the sidelines of the annual UN General Assembly.