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DAMASCUS, Syria — A defiant Bashar al-Assad expressed confidence that Syria's bloody war could be won within months, saying Russia's intervention has helped tip the scales toward victory.

Assad spoke exclusively to NBC News on Wednesday at his office in Damascus in a wide-ranging interview about the Syrian war, ISIS, the U.S. and his legacy.

He was unruffled by the State Department branding his vow to retake every inch of Syria as "delusional," saying it was only a matter of time until he regained full control of his country.

"The Syrian army has made a lot of advancement recently," Assad told NBC News. "It won't take more than a few months."

Assad's tone was strikingly different from a year earlier, when he was short of troops and losing territory to rebels and ISIS. The battlefield shifted, according to Assad, for one reason.

"The Russian support of the Syrian army has tipped the scales against the terrorists," he said. "It was the crucial factor."

His forces were teetering on the brink of defeat before Russia's military intervention got underway in September. Since then, they've made significant territorial gains — like retaking the ancient city of Palmyra from ISIS.