The State Department's No. 2 diplomat spoke with Iranian counterparts Monday about the crisis in Iraq, a senior State Department official said.
Deputy Secretary of State William Burns arrived in Vienna on Monday to join international negotiations on Iran's nuclear program, but with an expectation that he might speak on the sidelines of those talks about the threat posed by an Al Qaeda-inspired Sunni extremist group that has been seizing territory from the Iraqi government.
Late Monday night in Vienna, the senior State Department official said Burns and the Iranians did discuss Iraq on the sidelines of the nuclear meetings and that the two sides are open to more such discussions. The official spoke on condition of anonymity under ground rules set by U.S. officials.
The topic was not military coordination "or strategy determinations about Iraq's future over the heads of the Iraq people," the official said in a statement.
Instead, "we will discuss how [the Islamic State of Iraq and Syria, or ISIS] threatens many countries in the region, including Iran, and the need to support inclusivity in Iran and refrain from pressing a sectarian agenda."
U.S. and Iranian officials have been hinting for several days that they may discuss at least limited cooperation on how to deal with the extremist group, which has seized the Iraqi cities of Mosul and Tikrit in the last week.
The issue is a highly sensitive one. Though the U.S. and Iran back the Iraqi government, they have been at odds over their respective roles in Iraq and have widely divergent goals for the country.
U.S. allies Saudi Arabia and Israel fear any collaboration that could bring the United States and Iran closer together, weakening their strategic position against their top regional rival.
Analysts say the U.S. and Iran are likely to agree to only limited military cooperation at best, if President Obama chooses to order direct military action, such as airstrikes, in Iraq.
Washington and Tehran would probably want to share some information on their activities to avoid a direct conflict, they say.
U.S. officials do want to urge Iran not to further inflame the civil upheaval by mobilizing Shiite militias to attack Sunnis in Iraq. U.S. officials fear that the struggle is turning into a Shiite-Sunni sectarian fight that could set the entire Middle East ablaze.
The senior administration official dismissed the suggestion that collaboration between the countries could give Iran extra leverage in the ongoing negotiations over the Tehran regime's nuclear program.
"I don't see that at all," the official said.
The official predicted that the Iraq crisis would not affect the two countries' dealings on the nuclear issue, just as the U.S. and Russia continue to collaborate on the Iran nuclear issue despite their differences over the civil strife in Ukraine.
Burns is scheduled to sit in on a three-way meeting Monday between U.S., Iranian and European Union officials.
A respected diplomatic veteran, Burns was at the center of the secret bilateral negotiations between the United States and Iran that led to a November 2013 interim agreement on Iran's nuclear program.
He has handled the Iran file for the State Department for decades, and has the confidence of some Iranian officials.