The Islamic State group may have just lost the last major city of its self-proclaimed "caliphate", but experts and officials warn this is far from being the jihadists' deathblow.

Analysts say the Syrian army's recapture of Deir Ezzor announced Friday will push IS underground after losing territory once as large as Italy spanning the Iraq-Syrian border.

The most widely predicted scenario is that the group will transform into a guerrilla force on the ground in Sunni areas remaining outside the full control of Baghdad and Damascus.

At the same time, its "cyber-caliphate" will continue to churn out jihadist propaganda of the kind that inspired Tuesday's deadly truck attack in New York.

"Daesh is cornered," French Defence Minister Florence Parly said Tuesday, using an Arabic acronym for IS.

"It has lost its two capitals. The final offensives are under way to annihilate this pseudo-caliphate and its so-called soldiers," she told the Senate.

But she warned: "Daesh's swansong will be accompanied by new clandestine terrorist acts, sometimes spectacular ones, and the group's online influence will absolutely endure."

She pointed to Africa's unstable Sahel region along the southern rim of the Sahara, as well as Yemen, Nigeria, the Levant and the Philippines as areas where "the cancer of blind hatred is still spreading".

In Iraq, IS may have been drastically weakened, but "the military victory is not being accompanied by a political vision for after Daesh in terms of re-integrating the Arab and Sunni populations into politics," warned Jean-Pierre Filiu, a professor at Sciences Po university in Paris.

- 'From insurgents to terrorists' -

In Syria, he said, "the prospects are even worse".

"This absence of a long-term strategy leaves Daesh a lot of room for regrouping in the near future, while continuing to work its networks of supporters around the world."

Analysts expect IS to revert to tactics it used in its earlier incarnation as the Al-Qaeda in Iraq insurgency of 2004 to 2008.

In the coming months or years, they warn, it could potentially then re-emerge as a reinvigorated IS.

"There is unfortunately little doubt that IS, or something similar, will survive the worldwide campaign against it," Richard Barrett, a former British intelligence official, wrote in a report for the Soufan Group.

"There is little predictable about the trajectory of terrorism in a world in flux, except that it will continue to challenge international security for many years to come."

He said surviving members of what was once a 40,000-strong force of foreign fighters from more than 100 countries were among the main threats.

Some are now imprisoned in Syria and Iraq; others will be heading home.

"These recruits may also decide to seek new theatres of jihad once they have rested and recuperated," the report warned.

Colin P. Clarke, a terrorism expert at the RAND Corporation, said IS "is being forced to change its strategy and tactics, but it has been proactively preparing for the next phase of the conflict".

"In short, it is transitioning from an insurgent organisation to a terrorist group," he wrote in a blog post.

The world is watching it shift from being "an insurgent organisation with fixed headquarters to a clandestine terrorist network dispersed throughout the region and the globe", he said.

source: AFP