Presence of Iranian Advisors in Iraq Battle 'Concerning' to US: Ashton Carter

The presence of Iranian advisers in the Iraq battle for Tikrit is "concerning" to the United States, Secretary of Defense Ashton Carter said Wednesday.

A mostly Shiite Iraqi force, including Iranian-backed militias, entered Tikrit Wednesday from the Islamic State group after a 10-day push to enter the city.

The presence of Iranian military advisers in that force "is something that is concerning to us in particular because the sectarian danger in Iraq is the principal thing that can unravel the campaign against ISIS," Carter said using another name for IS.

Iran backs a number of militias that are fighting the radical group IS which holds large swaths of Iraq and Syria.

The US is also leading a coalition of forces in an air campaign against IS, and Carter emphasized that the battle against the group was not only led by Iran.

"There are actually several important battles going on, in some of which the Iranians play no role at all," Carter said.

Soldiers, police officers and militiamen took part in the campaign to retake Tikrit and entered parts of the city Wednesday and are still battling to control it. Tens of thousands of fighters are facing off with hundreds of jihadists, military sources said.