Kurdish-led forces pronounced the death of the Islamic State group's nearly five-year-old "caliphate" Saturday after flushing out diehard jihadists from their very last bastion in eastern Syria.

Fighters of the US-backed Syrian Democratic Forces raised their yellow flag in Baghouz, the remote riverside village where diehard jihadists of a variety of nationalities made a desperate, dramatic last stand.

The SDF's victory capped a deadly six-month operation against the final remnants of the caliphate which once stretched across a vast swathe of Iraq and Syria, and held seven million people in its sway.

World leaders hailed the victory as a major landmark in the fight against IS and its ideology, but warned the group that spurred a spate of global terror attacks was far from defeated.

"Syrian Democratic Forces declare total elimination of so-called caliphate and 100 percent territorial defeat of ISIS," spokesman Mustefa Bali said in a statement, using another acronym for IS.

In Al-Omar, an oil field used as the main SDF staging base for the final phase of the assault, fighters in their best fatigues laid down their weapons and broke into song and dance.

They joined top Kurdish and Arab tribal officials, as well as a leading US envoy, for a ceremony unveiling a monument to their fallen comrades and celebrating the landmark victory.

The state proclaimed in mid-2014 by fugitive IS supremo Abu Bakr al-Baghdadi started collapsing in 2017 when parallel offensives in Iraq and Syria wrested back its main hubs Mosul and Raqa.

The nearly five years of fighting against the most brutal jihadist group in modern history left thousand-year-old cities in ruins and populations homeless.

- Foreigners last -

Early US estimates put the numbers of IS fighters at around 40,000, many of them foreigners.

The territory administered by the remnants of IS continued to shrink month after month and in September 2018 the SDF launched a final offensive on the last dregs of the "caliphate" in its Euphrates Valley strongholds.

SDF fighters last week expelled the last IS fighters who refused to surrender from an encampment on the edge of Baghouz and have since been hunting down a few survivors hiding on the reedy banks of the Euphrates.

"Those who lasted the longest were mostly foreigners... Tunisians, Moroccans, Egyptians," Hisham Harun, a 21-year-old Kurdish fighter, told AFP.

Around him, the former jihadist encampment was littered with bullet-riddled truck carcasses, discarded suicide belts and the torn tents where the caliphate's last families sheltered for weeks.

Some bodies of suspected IS fighters could also be seen.

According to the Syrian Observatory for Human Rights, the Euphrates offensive has left 630 civilians, 730 SDF fighters and around 1,600 jihadists dead.

Kurdish officers and aid groups were flummoxed by the number of people who had remained holed up in the last IS redoubt of Baghouz, a small village even few Syrians had ever heard of until this year.

As SDF forces pummelled IS positions and US warplanes dropped huge payloads on the riverside village, tens of thousands of people fled over a rocky hill.

- Aid emergency -

For weeks, the ghostly figures of the caliphate's last denizens hobbled out of the besieged village, famished, often wounded but sometimes still defiantly proclaiming their support for IS.

The Kurdish-led force and foreign intelligence have screened more than 60,000 people since January, around 10 percent of them jihadists turning themselves in.

Most of the people evacuated from the smouldering ruins of Baghouz in recent days were relatives of IS members who now fill overcrowded camps further north in Syria's Kurdish-controlled region.

The biggest of them, Al-Hol, is struggling to host 74,000 people, including at least 25,000 school-aged children.

Among them are thousands of foreigners from France, Russia, Belgium and 40-plus countries that are in most cases unwilling to take them back.

"The needs are huge and the camp is overwhelmed," Peter Maurer, president of the International Committee of the Red Cross said Friday upon returning from a five-day visit to Syria.

- Still a threat -

Speaking at the ceremony in Al Omar, top SDF commander Mazloum Kobane warned that a new phase had begun in anti-IS operations.

The US has vowed to draw down its forces in Syria, but Kobane appealed for sustained coalition assistance to help smash sleeper cells "which are a great threat to our region and the whole world."

US coalition envoy William Roebuck spoke after him at the ceremony and agreed "we still have much more to do to achieve an enduring defeat" of IS.

French President Emmanuel Macron hailed the fall of Baghouz saying "a significant threat to our country" has been "eliminated" and British Prime Minister Theresa May chimed in, calling Saturday's victory "a historic milestone".

The jiahdists retain a presence in eastern Syria's vast Badia desert and various other hideouts from which they could wage the kind of deadly guerrilla insurgency that accompanied the rise of the Islamic State group.

John Spencer, a scholar at the Modern War Institute at West Point, warned that while the geographic caliphate had been dismantled, IS was far from defeated.

IS "is a terrorist organisation, all they have to do is put down their weapons and try to blend in with the population and just escape," he told AFP. "They're not gone, and they're not going to be gone."

HM