The Islamic State (ISIS/ISIL) in Iraq cut one ear off 33 jihadists it caught deserting the Mosul battlefield, where U.S.-backed local troops are engaged in a fierce fight against the terrorist organization, an Iraqi news outlet has learned.

A security source in northern Iraq’s Nineveh province told the Arabic-language Alsumaria News on condition of anonymity, “The leadership of the extremist group threatened to cut both ears if the escapes are repeated.”

The source revealed that the deserters spent time behind bars before their fellow jihadists carried out their punishment.

ISIS is notorious for brutally punishing deserters.

Mosul, the capital of Nineveh, is considered ISIS’s last major stronghold. The fight to push ISIS out of the city, the second-largest in Iraq, has been raging since mid-October 2016.

Throughout the Mosul fight, ISIS has been executing jihadists who flee the battle. Alsumaria’s source indicated that the new punishment is a sign that the terrorist group’s ranks are dwindling.

At the end of February, Alsumaria revealed that ISIS chief Abu Bakr al-Baghdadi had admitted defeat in Mosul in a “farewell speech” that urged the group’s jihadists in the battlefield to “flee and hide” or “ blow themselves up when surrounded by Iraqi forces.”

Iraqi Brig. Gen. Yahya Rasool recently said that ISIS currently controls less than a quarter of the land it held at its peak in 2014. ISIS terrorists controlled more than 40 percent of Iraq at that time.

“As of March 31, they only held 6.8 percent of Iraqi territory,” revealed the Iraqi general.

ISIS still controls the towns of Qaim, Tal Afar, and Hawija in Iraq, in addition to Raqqa in Syria, which serves as the jihadist organization’s de-facto capital.

U.S.-backed Iraqi government troops have been fighting ISIS in Mosul with the help of their allies, which includes tens of thousands of Kurdish Peshmerga forces, Iran-allied Shiite fighters, Sunni tribesmen, and Christian militiamen, among others.

The Iraqi coalition managed to push the terrorist group out of eastern Mosul in January, but it has “been bogged down by bloody close-quarters fighting through the maze-like streets” of the western half of the city, notes Daily Mail.

“The federal police said in a statement on Tuesday they have been reinforcing their positions in Western Mosul in preparation for a push on the al-Nuri Mosque where Islamic State leader Abu Bakr al-Baghdadi declared a caliphate in 2014,” it adds.