About 12,000 foreigners from as many as 40 countries -- 4,000 women and 8,000 children -- are stranded in those countries.

Most are in the Al-Hol camp in northeastern Syria, where the Kurdish authorities are pressing for them to be returned to their countries of origin.

Here is a round-up of how various countries are dealing with the issue.

- Russia, Kosovo first -

Nearly 4,500 Russian citizens went to fight alongside the IS, and Moscow was the first to organise returns more than a year ago.

By February around 200 women and children had returned, originating mainly from Russia's Islamic republics in the Caucasus.

Moscow estimates that nearly 1,400 children are still stranded.

Kosovo, which is 90 percent Muslim, announced in April it is repatriating 110 nationals from Syria, almost all wives and children of jihadists.

- France, Belgium: case by case -

Paris has said it is studying the files of all of its citizens held in northeastern Syria on a case-by-case basis.

Amid hostile public opinion, 12 orphaned children of French jihadists were flown back from Syria on June 10.

France also repatriated five orphans from Syria in mid-March, as well as a three-year-old girl whose mother was sentenced to life imprisonment in Iraq.

Like France, Belgium has been one of the biggest sources of foreign fighters for IS.

The authorities recorded more than 400 travelling from 2012.

According to Belgian press reports, between 50 and 60 minors are still in three Kurdish-run camps in Syria.

On Thursday, Belgium said it will bring six orphans home from Kurdish-controlled camps in Syria, four of whom are older than 10.

- Germany: children repatriated -

A dozen children of jihadist fighters have been repatriated from Iraq to Germany since March.

The German authorities say the children are "victims" and they should return if they have family to take them in.

Children who have been radicalised will be placed in a special institution but not be locked up.

- Denmark: stripped of nationality -

The government in late March drew up draft legislation under which children born abroad to jihadists will not have Danish nationality.

- United States -

Washington has urged Western countries to take their nationals back and started repatriating some of its own.

Two American women and six children from families of suspected IS members were repatriated in early June.

In July 2018 Washington brought home three IS fighters for prosecution and also repatriated a woman with her four children.

- Britain -

London says it is looking into ways of bringing home British children but it does not want to encourage the return of adults and has stripped some IS proponents of citizenship.

The hardline stance drew criticism in March when 19-year-old Shamima Begum, who ran away to join the IS in Syria, lost her British citizenship.

- Tunisia: no repatriation -

About 5,000 Tunisians joined the IS in Syria and Libya, according to the UN in 2015.

No children have been brought home from Syria or Iraq, according to Human Rights Watch in February.

Tunisia's government worries that repatriating children will accelerate the return of their jihadist parents, according to local rights activists.

- Turkey -

In late May, Iraq repatriated to neighbouring Turkey 188 children of Turks accused of belonging to IS, a capital offence in Iraq.

- Tajikistan, Uzbekistan -

Tajikistan, from where more than 1,000 travelled to fight for IS, said in May that 84 children had been brought back from Iraq.

On May 30, Uzbekistan said it had repatriated 156 nationals, mostly women and children.