Former CIA chief Michael Hayden said Tuesday he was “uncomfortable” with Iran’s growing influence in Iraq, made especially evident by an offensive in Tikrit, reports the AFP news agency.

The city, which is the home town of former president Saddam Hussein, is the target of as assault led by Iraqi troops and Shiite militias backed by Tehran.

“I am made uncomfortable by the growing Iranian influence in Iraq. I am made uncomfortable by the fact that it looked like a Shia advance against a Sunni town,” said Hayden, who headed the Central Intelligence Agency between 2006 and 2009.

“And the proof would be what happens if and when they retake Tikrit… How the militias act toward the local population,” he added, during a roundtable on international intelligence sharing at the New America Foundation.

Hayden said the United States should not be sharing intelligence with the Iranians on Iraq, despite their shared desire to wipe out the Islamic State (ISIS) group.

“The Islamic republic’s ultimate objective is different,” he explained, adding,  “We are looking for an inclusive government with minority rights and the participation of all the major religious and ethnic groups.”

“It’s clear to me that the Iranian policy is based upon Shia dominance of the new Iraqi state, and that effort in itself feeds the Sunni opposition, which ISIL then lives off of to resurrect their movement,” Hayden added, using an alternative acronym for the Islamic State group.

Some 30,000 men have been involved in a week-old operation to recapture Tikrit, one of the ISIS fighters’ main hubs since they overran large parts of Iraq nine months ago.

Iran has been involved in the fight against ISIS before, having bombed the group’s jihadists in eastern Iraq in late 2014, an attack which the Pentagon clarified was not coordinated with the United States.

The reports about Iran’s involvement in the airstrikes on ISIS come amid speculation of U.S. military cooperation with the Islamic regime, after Secretary of State John Kerry backtracked and said the U.S. couldn’t rule out cooperation, and President Barack Obama secretly wrote to Iranian Supreme Leader Ayatollah Khamenei in mid-October urging him to join the coalition against ISIS.

According to reports, though Iran initially rejected the notion of such cooperation against ISIS, with Khamenei saying he rejected the idea because of Washington’s “dirty hands”, Tehran later said it would consider it – in return for a good deal in the nuclear talks.