Factbox-After the fall, Islamic State strikes from Iraq and Syria hinterlands

A view of the old city of Mosul and buildings destroyed during past fighting with Islamic State militants, in Mosul, Iraq February 1, 2022. REUTERS/Khalid al-Mousily

ISTANBUL (Reuters) - Nearly three years after their self-declared caliphate was dismantled and their forces defeated in a battle by the Euphrates river, Islamic State fighters are waging a guerrilla campaign from remote regions of Iraq and Syria.

The March 2019 battle of Baghouz, by the Syria-Iraq border, ended Islamic State control which once extended across swathes of both countries, including the cities of Raqqa and Mosul.

It also completed the group's strategic shift from a force which had ruled over the daily lives of millions of people back to an insurgency launching attacks from the shadows.

Here is a summary of Islamic State's status in Iraq and Syria.

LEADERSHIP AND STRUCTURE

After the killing of Islamic State founder Abu Bakr al-Baghdadi in October 2019, the group named his successor as Abu Ibrahim al-Hashemi al-Quraishi.

Beyond Quraishi, an Iraqi who was once held in U.S. custody, little is know of Islamic State's leadership - partly because it now operates in a secretive structure of autonomous local cells, rather than the centralised administration of the "caliphate".

Last year Iraq captured Sami Jasim, another Iraqi national who was a deputy to Baghdadi and a close aide to Quraishi, in northern Syria with Turkish help.

The U.S.-led coalition fighting Islamic State said in mid-2019, after the last stand in Baghouz, that the group retained 14,000 to 18,000 members, including 3,000 foreigners, though there have been other varied estimates.

Analysts say many local fighters may have slipped back into normal life, ready to re-emerge when the opportunity comes.

"This is an organisation that has retained a significant amount of manpower," said Charles Lister of the Washington-based Middle East Institute. "In terms of kinetically operating cells, I imagine we are talking in the very low thousands in both countries together. But it's virtually impossible to measure."

ATTACKS

Islamic State fighters attacked a jail holding militants in the northeastern Syrian city of Hasaka nearly two weeks ago, their biggest operation since the defeat of their caliphate.

Kurdish-led Syrian Democratic Forces who control the area said 40 of their troops, 77 prison guards and four civilians were killed, as well as 374 Islamic State attackers or detainees, in the attempted jail break.

Also in late January, IS fighters attacked an Iraqi army base in Diyala, northeast of Baghdad, killing 11 soldiers.

Meanwhile it has continued targeted assassinations, ambushes, suicide bombings and lesser noticed - but daily - attacks with improvised explosive devices.

The latest U.S. government report said Islamic State claimed 182 attacks in Iraq and 19 in Syria over a three-month period. While that was lower than previously, the report noted the group was still able to carry out lethal and complex operations.

"What we have seen in the last six to 12 months, on both sides of the Syrian and Iraq border, is that (IS) cells have been more willing to launch bolder raids," Lister said.

BASES

Syria's 11-year civil war and Iraq's turbulence since the 2003 U.S.-led invasion have provided fertile ground for Islamic State to embed in populations alienated by political corruption, violence, insecurity and ethnic or religious divisions.

In Iraq, the hinterlands between central government control and the Kurdish regional government in the north offer opportunities for the group to evade capture.

Areas of Syria's eastern desert outside government control also provide a haven for Islamic State, while Syrian Kurdish-led forces that rule northeast Syria are ill-equipped for a counter-insurgency role needed to keep the group from regrouping.

FUTURE STRATEGY?

Islamic State's past may offer clues to it future plans.

Its predecessor, Islamic State in Iraq, was largely crushed in 2007-9 when the United States reinforced troops and allied them with local fighters to put down that insurgency.

The group went underground, playing a long game until growing disenchantment among Iraq's Sunni Muslim population at the Shi'ite-led government in Baghdad, combined with the conflict in neighbouring Syria, offered fresh opportunity.

In 2012 and 2013, in a series of operations similar to this month's Hasaka attack, Islamic State targeted prisons in western and southern Iraq and released hundreds of detainees including prominent militants.

At the same time, using intimidation, extortion and theft they gained resources and power over local populations - preparing them for the moment in 2014 when they seized control of the city of Mosul and a large part of northern Iraq.

(Reporting by Dominic Evans; Editing by Mike Collett-White)