The top tier of the 52m Malwiya tower was blown off in an attack by fighters, said police Lieutenant Colonel Mahmud Muhammad on Friday.
The explosion left debris on the tower's winding ramps and a jagged hole on the top level, an AFP reporter said. The unique yellow sandstone tower in Samarra, an ancient city on the banks of the Tigris river, was completed in 850 CE by the Islamic Abbasid dynasty.
US troops had been stationed in the tower until two weeks ago. US and Iraqi troops had draped an Iraqi flag from the minaret after retaking Samarra from rebels last October, and locals accused US forces of using it as a sniper position.
The minaret, considered an architectural wonder, was built by Abbasid ruler or Caliph al-Mutawakkli after the dynasty made Samarra the seat of the Islamic world in the 8th century.
Iraq proposed that Unesco make the minaret a world heritage site in 2000. Famed British archaeologist Sir Mortimer Wheeler once paid a lavish tribute to the Malwiya minaret. "What matters most about the Samarra minaret is not its formal design, but its startling originality. Strikingly bold and simple in design, functional, elemental, finely proportioned, comfortable to the eye.
"Here we have in the ninth century many qualities which bridge the centuries. The Malwiya is truly a great and rather lonely masterpiece."
Many of Iraq's archaeology sites have been plundered by thieves or damaged by US-led military operations since the US invasion two years ago.