The United States discussed the crisis in Iraq with Iran on the sidelines of nuclear talks in Vienna, U.S. officials said Monday, warning that no outside countries can fix the country's problems.

Jihadists of the Islamic State of Iraq and the Levant (ISIL) have taken control of a swath of territory north of Baghdad in a drive towards the Iraqi capital launched a week ago, leading to growing fears that the country is sliding towards chaos.

"The issue did come up briefly with Iran on the margins of the P5+1 in Vienna today, separate from our trilateral meeting" which had included the EU, a senior State Department official said in a statement, asking not to be named.

State Department deputy spokeswoman Marie Harf confirmed to CNN television that there were "brief discussions."

It is yet to be determined "if we want to keep talking to Iran about Iraq," she added, acknowledging though that Tehran and Washington had "a shared interest" in ensuring that militants don't get "a foothold any more in Iraq."

But she stressed: "No outside country can fix Iraq's problems. We need Iraq's political leaders from across the spectrum to step up."

U.S. President Barack Obama meanwhile said about 275 US military personnel were being deployed to protect the American embassy in Baghdad.

The force, which began deploying on Sunday, has been sent "for the purpose of protecting U.S. citizens and property, if necessary, and is equipped for combat," Obama wrote in a letter notifying U.S. lawmakers.

Another U.S. official told AFP no further bilateral talks on Iraq were likely to be held in Vienna, but did not rule out further discussions elsewhere between the traditional foes.

US and Iranian delegations are already in Vienna for talks on hammering out a treaty to rein in Tehran's nuclear ambitions with global partners from the grouping known as the P5+1.

Any further bilateral "engagements" on Iraq "will not include military coordination or strategic determinations about Iraq's future over the heads of the Iraqi people," the State Department official said in the statement.

"We will discuss how ISIL threatens many countries in the region, including Iran, and the need to support inclusivity in Iraq and refrain from pressing a sectarian agenda," the State Department statement said.