​Iran seen as critical in pushing ISIS out of Tikrit

KIRKUK, Iraq -- In a new, slickly produced video, ISIS claims its militants are still on the streets of Tikrit -- confidently fighting off the assault by Iraqi forces.

But in Tikrit's outskirts, Iraqi soldiers are trying to encircle the extremists - and they're being helped by troops from Iran, with an Iranian general reportedly commanding the battle.

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ISIS video claiming to show their militants fighting off the assault by Iraqi forces

That's raised fears in the U.S. about Iran's rising influence - but with nearly a third of Iraq now in the grip of ISIS, many Iraqis welcome the Iranian intervention.

Iraq's main North-South highway is in ISIS-controlled territory. The Iraqi forces - and the Iranian soldiers fighting alongside them - need to recapture that road to secure a supply route from Baghdad.

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CBS News correspondent Holly Williams reporting near the front lines of the fighting to regain Tikrit in Iraq CBS News

"Iraqi forces alone, they cannot do this," said Dr. Najmaldin Karim, the governor of Iraq's war-torn Kirkuk Province. "There's no denying to that and if Iran is helping with whatever way I don't see how you can say no to them."

Karim told us that even if Tikrit is recaptured, ISIS is a very long way from defeat.

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Dr. Najmaldin Karim, the governor of Iraq's war-torn Kirkuk province. CBS News

"They have this ability to move around," Karim said. "We cannot take it lightly that just because you take them out of a place, that's it, that place is safe and they will never come back."

Secretary of State John Kerry said Thursday that the U.S. still considers Iran to be a state sponsor of terrorism. But earlier this week General Martin Dempsey, the Chairman of the U.S. Joint Chiefs of Staff, said that Iranian involvement in Iraq might be a positive thing.