Sources tell Reuters U.S. and Iranian officials met on Monday in Vienna, where they discussed the security situation in Iraq.

The talks happened on the sidelines of separate nuclear negotiations.

Both the U.S. and neighboring Shiite Iran have been alarmed by the stunning advance of Sunni insurgents in Iraq.

The militants have swept through northern Iraq in just one week.

So alarmed, there was talk that Washington and Tehran -- adversaries for decades -- might cooperate with a military response.

But earlier on Monday, U.S. State Department spokeswoman Jen Psaki said any potential talks with Iran would NOT involve military cooperation.

(SOUNDBITE) (English) JEN PSAKI, U.S. STATE DEPARTMENT SPOKESPERSON, SAYING:

"I would remind you that we've had similar conversations in the past with Iran, regarding Afghanistan. These consultations would be along those lines. We're not talking about coordinating any military action in Iraq, with Iran."

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