The leader of the Islamic State of Iraq and the Levant (ISIL) terrorist group, also known as the Islamic State of Iraq and Syria (ISIS), Islamic State (IS), and by its Arabic language acronym, Ibrahim al-Samarrai, also known as Abu Bakr al-Baghdadi, has reportedly fled Iraq's Mosul for his life, leaving the battle to the group's operational commanders.

Media reports say that U.S. and Iraqi officials believe Abu Bakr al-Baghdadi has left operational commanders behind with diehard followers to fight the battle of Mosul, and is now hiding out in the desert, focusing mainly on his own survival.

Reuters notes that it is impossible to confirm the whereabouts of the Islamic State "caliph", who declared himself the ruler of all Muslims from Mosul's Great Mosque after his forces swept through northern Iraq in 2014.

But U.S. and Iraqi intelligence sources said on March 8 that an absence of official communication from the group's leadership and the loss of territory in Mosul suggest he has abandoned the city, by far the largest population center his group has ever held.

He has proved to be an elusive target, rarely using communication that can be monitored, and moving constantly, often multiple times in one 24-hour cycle, the sources say, according to Reuters.

From their efforts to track him, the intelligence sources reportedly believe he hides mostly among sympathetic civilians in familiar desert villages, rather than with fighters in their barracks in urban areas where combat has been under way.

ISIL never commented, for example, on the capture of the eastern half of Mosul by Iraq's 100,000-strong forces in January.  And Baghdadi himself has not released a recorded speech since early November, two weeks after the start of the Mosul battle.

But he has proved to be an elusive target in the past, rarely using communication that can be monitored, and moving constantly.

The group's presence on Telegram, a social media network that had become its main platform for announcements and speeches, has tapered off.  The coalition estimates that ISIL activity on Twitter has fallen by 45 percent since 2014, with 360,000 of the group's Twitter accounts suspended so far and new ones usually shut down within two days.

Baghdadi has not publicly appointed a successor, but Iyad al-Obaidi, also known as Fadel Haifa, a security officer under former dictator Saddam Hussein, is known to be the de facto deputy, according to Iraqi intelligence sources, Reuters noted.

More than 40 leading members of the group have been killed in coalition air strikes, but the insurgency is likely to continue even if Mosul is captured and Baghdadi and his aides are killed, according to Iraqi security experts.