Abu Bakr al-Baghdadi
Abu Bakr al-BaghdadiReuters

Abu Bakr al-Baghdadi, the elusive leader of the Islamic State (ISIS) jihadist group, has escaped numerous assassination attempts by US forces since declaring his so-called "Caliphate" over vast swathes of Iraq and Syria in 2014.

Until recently, US intelligence officials believed the wanted jihadist leader - who has a $25 million bounty on his head - was hiding out in a bunker somewhere in Raqqa, ISIS's "capital" city. 

Since an appearance at the central mosque for a Ramadan sermon in Mosul, Iraq two years ago, the self-proclaimed "Caliph Ibrahim" hasn't been seen in public, and his last audio message was released late last year, indicating just how carefully he is trying to avoid the fate of his predecessors during the jihadist insurgency against the US in Iraq, who were assassinated by US airstrikes.

Densely-populated Raqqa would theoretically pose a perfect place to hide: deep inside ISIS territory, surrounded by civilians, Baghdadi could feel safe that the major potential for massive civilian casualties and operational difficulties mounting a special forces assault would keep him safe even after his group claimed responsibility for Sunday's massacre at a nighclub in Orlando, Florida.

But according to security officials who spoke to CNN, US intelligence assessments are moving away from the Raqqa theory - though they are not discounting it - and towards the possibility that Baghdadi is spending his time constantly on the move throughout ISIS territory in Iraq and Syria.

In the words of one US official, the ISIS leader is practicing "extraordinary operational security" measures to avoid leaving himself open to becoming a target.

According to the CNN report, intelligence reports suggest Baghdadi traveled to Mosul at least twice over the past six months, bolstering the theory that he is constantly on the move.

US intelligence officials say the theory began being carefully considered after they noted that despite "mapping out" the ISIS leadership - and killing and capturing several senior ISIS commanders over the past year - there appears to be no trace of Baghdadi's whereabouts.

Even when leading ISIS commander were assassinated, intelligence services waited in vain for Baghdadi to surface and attempt to switch location - indicating again that he may not be in the area they believe him to be.

But the Pentagon is hopeful of gaining a lead.

According to US Special Envoy Brett McGurk, al-Baghdadi may be forced into appearing publicly in the coming weeks in honor of Ramadan. Not doing so would be a symbolic blow to the self-proclaimed "leader of all Muslims"; Baghdadi has already been mocked and lambasted by some Muslim scholars, who note that according to Islamic practices a Caliph is supposed to be accessible to the masses.

"It is Ramadan. He purports to be the caliph - that's what he calls himself - and so you would think he'd be coming out with a statement to his - to his so-called followers," McGurk said.