US Secretary of State John Kerry.

WASHINGTON: US Secretary of State John Kerry said Monday he would be open to cooperating with Washington’s traditional foe Iran on Iraq, and warned drone strikes were an option to halt a militant assault.

“I wouldn’t rule out anything that would be constructive,” Kerry told Yahoo News when asked if the United States would cooperate militarily with Iran, one of Iraqi Prime Minister Nuri Al-Maliki’s key allies.

He stressed, however, “Let’s see what Iran might or might not be willing to do before we start making any pronouncements.”

Even though Iran and the United States do not have formal diplomatic ties, talks between US and Iranian officials could come as early as this week on the sidelines of scheduled negotiations on Tehran’s nuclear ambitions in Vienna.

Significantly, Kerry’s deputy Bill Burns who led months of secret talks with Iran in Oman to kickstart the nuclear negotiations, is with the US delegation in Austria, signalling that separate discussions could be on the table.

US President Barack Obama is carrying out “a very thorough vetting of every option that is available” including drone strikes, Kerry said, stressing Washington was “deeply committed to the integrity of Iraq as a country.”

A week after extremists from the Islamic State of Iraq and the Levant captured Iraq’s second city Mosul in a lightning sweep, the jihadists and security forces were Monday battling for control of the strategic Shiite town of Tal Afar.

The stunning offensive appears to have caught Iraqi leaders and Washington by surprise, and prompted fears of a possible new sectarian civil war between Sunni and Shiites in the country from which US forces withdrew in December 2011.

“This is a challenge to the stability of the region. It is obviously an existential challenge to Iraq itself. This is a terrorist group,” Kerry told Yahoo.

Kerry agreed that drones might not be 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.”

Amid reports of a massacre of 1,700 Shiite soldiers by the Sunni militants, Kerry insisted “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 have try to stop it from the air or otherwise.”

On talks with Iran, the top US diplomat also said that Washington would “be open to any constructive process here that could minimize the violence, hold Iraq together, the integrity of the country and eliminate the presence of outside terrorist forces that are ripping it apart.”

“I wouldn’t rule out anything that would be constructive to providing real stability, a respect for the constitution, a respect for the election process, and a respect for the Iraqi people to form a government that represents all of the interests of Iraq — not one sectarian group over another.”

But he stressed he did not believe in the short-term that ISIL could take the Iraqi capital, and insisted Washington was watching the situation closely and taking precautions to protect the US embassy.

The State Department said Sunday that some of its embassy staff were being relocated to other consulates in Iraq as well as Jordan.