The threat of fresh attacks on the West by foreign fighters fleeing the fallen Islamic State stronghold of Raqa is set to dominate a G7 meeting of interior ministers in Italy.
The two-day gathering, which kicked off Thursday on the Italian island of Ischia, comes just days after US-backed forces took full control of the jihadists' de facto Syrian capital.
Most foreign fighters are believed to have fled over the past few months. Experts say those who stayed are now likely to head for Turkey in the hope of travelling on to Europe to seek revenge for the destruction of the "caliphate".
The interior ministers of the Group of Seven --- Britain, Canada, France, Germany, Italy, Japan and the US -- arrived Thursday shortly before sundown at a medieval castle on the island off Naples.
They walked along a land bridge to the castle, which sits off the coast, before heading through narrow cobbled streets to a gala dinner.
The working sessions were due to kick off on Friday morning.They were joined by the EU commissioner for migration Dimitris Avramopoulos, European safety commissioner Julian King and Juergen Stock, secretary general of Interpol.
Tens of thousands of citizens from Western countries travelled to Syria and Iraq to fight for the group between 2014 and 2016, including extremists who then returned home and staged attacks that claimed dozens of lives.
While border crossings have since tightened making it more difficult for fighters to return, security experts have warned of renewed possibilities of strikes as the pressure on IS intensifies.
- Boats to Europe -
"With an Islamic military defeat in Iraq and Syria we could find ourselves facing a return diaspora of foreign fighters," Italy's Interior Minister Marco Minniti told a parliamentary committee last week.
"There are an estimated 25,000 to 30,000 foreign fighters from 100 countries. Some of them have been killed of course, but... it's possible some of the others will try to return home, to northern Africa and Europe," he said.
The Syrian Observatory for Human Rights, a Britain-based monitor of the war, said a group of 130-150 foreign fighters, including Europeans, had turned themselves in before the end of the battle in Raqa.
Other reports suggested a convoy of foreign fighters had been able to escape the city towards IS-held territory, a claim denied categorically by Syrian Democratic Forces (SDF) officials.
The SDF is expected to contact the home countries of any foreign fighters it holds, to discuss the possibility of turning them over to face prosecution.
But captured fighters could prove a legal headache, with questions raised over what evidence, collected by whom, would be used in a domestic court. Jihadists also become security risks in jails for their potential to radicalise.
"We need to set up a large de-radicalization project, we'll talk about it in Ischia," Minniti said.
French European lawmaker Arnaud Danjean said Wednesday there would be "negotiations with the countries concerned" over what to do with returnees.
Minniti warned fighters could take advantage of the confusion and "use the human trafficking routes" to return home -- raising the spectre of extremists embarking on the migrant boats which regularly head to Italy.
"Before, they wouldn't have risked a precious assest, a trained fighter cell, ending up on a sinking boat in the Mediterranean. Now that they're on that run that's changed," he said.
It meant controversial efforts currently spearheaded by Italy to close the land and sea trafficking routes which cross Africa into Libya and on across the central Mediterranean sea to Europe were "essential", he added.
- Terrorism online -
The Group of Seven will also tackle the hot issue of terrorism online, with analysts warning IS's loss of territory will turn street-to-street fighting into an intelligence war.
In a G7 first, representatives from Internet giants Google, Microsoft, Facebook and Twitter will also be taking part as the interior ministers want the tech giants to go further and faster in identifying extremism..
"The internet plays a decisive role in radicalization. Over 80 percent of conversations and radicalisation happen online," said Minniti.