WASHINGTON (AP) — The Obama administration is willing to talk with Iran over deteriorating security conditions in Iraq and is not ruling out potential U.S.-Iranian military cooperation in stemming the advance of Sunni extremists, Secretary of State John Kerry said Monday.

Kerry also said in an interview with Yahoo! News that U.S. drone strikes “may well” be an option.

Kerry said Washington is “open to discussions” with Tehran if the Iranians can help end the violence and restore confidence in the Iraqi government. Asked about possible military cooperation with Iran, Kerry said he would “not rule out anything that would be constructive.” However, he stressed that any contacts with Iran would move “step-by-step.”

U.S. officials said earlier there is a possibility that Undersecretary of State William Burns may discuss Iraq with an Iranian delegation at nuclear talks in Vienna.

“We’re open to discussions if there is something constructive that can be contributed by Iran, if Iran is prepared to do something that is going to respect the integrity and sovereignty of Iraq and ability of the government to reform,” Kerry said.

The Obama administration is also considering unilateral airstrikes to slow an al-Qaida-inspired insurgency that is threatening the government of President Nouri al-Maliki.

Kerry said Monday those are still an option.

“They are not the whole answer, but they may well be one of the options that are important to be able to stem the tide and stop the movement of people who are moving around in open convoys and trucks and terrorizing people,” he said. “When you have people murdering, assassinating in these mass massacres, you have to stop that and you do what you need to do if you need to try to stop it from the air or otherwise.”

In the last week, Sunni militants took Iraq’s second-largest city, Mosul, and Saddam Hussein’s hometown of Tikrit in a lightening offensive that has plunged Iraq into its worst crisis since the 2011 withdrawal of U.S. troops. Over the weekend, militants posted graphic photos that appeared to show their gunmen massacring scores of captured Iraqi soldiers.

With Baghdad threatened by the militants’ advance, the State Department reinforced security at the U.S. Embassy and sent some personnel out of town.

Much of the embassy staff will stay in place, State Department spokeswoman Jen Psaki said in a statement released Sunday. The statement did not say the number of personnel affected. The embassy, along the Tigris River in Baghdad’s Green Zone, has about 5,000 personnel and is the largest U.S. diplomatic post in the world.

Some embassy staff members were being temporarily moved elsewhere to more stable places at consulates in Basra, in the Shiite-dominated south of Iraq, and Irbil, in the Kurdish semi-autonomous region in northeastern Iraq, and to Jordan, she said.

U.S. travelers in the country were encouraged to exercise caution and limit travel to certain parts of Iraq.

Pentagon spokesman Rear Adm. John Kirby said in a statement that a “small number” of military personnel are helping to keep State Department facilities in Baghdad safe. He said embassy personnel are being moved by commercial, charter and State Department aircraft, adding that the U.S. military has “airlift assets at the ready” should the State Department request them.

A U.S. military official said about 100 Marines and Army soldiers have been sent to Baghdad to help with embassy security.

Defense Secretary Chuck Hagel has ordered the aircraft carrier USS George H.W. Bush and the amphibious transport dock ship USS Mesa Verde to the Persian Gulf as the president considers possible military options for Iraq. Kirby said the moves will give Obama additional flexibility if military action were required to protect American citizens and interests in Iraq.

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Associated Press writers Lolita C. Baldor, Kimberly Hefling in Washington and George Jahn in Vienna contributed to this report.