London, UK - A fractured flag of Syria is projected on to screens hanging on the eight-metre-high wall behind the stage as Arabic music from an ISIL video fills the theatre.

Three women whose children have all left Molenbeek, Belgium, to join the Islamic State of Iraq and the Levant (ISIL, also known as ISIS), each take a seat on chairs set up in a triangle.

It is the start of a powerful play at London's National Theatre - Another World: Losing Our Children to Islamic State.

The play is verbatim, documentary theatre: All of the actors' words - their umms and ahhs, laughter and tears - were uttered by real people in months of interviews with writer Gillian Slovo.

The idea for the play, which runs until May 7, came from a desire to know more about ISIL, Slovo said in an interview at the theatre, overlooking a rain-splattered River Thames.

Slovo said she and director Nicolas Kent "were watching the news and seeing this seemingly new phenomenon that was incomprehensible.

"Not just Islamic State itself, but the fact that young people who are from our society should choose to go and join that murderous regime. So it felt like if we wanted to know more, then there was an audience out there that would also want to know more," said Slovo, 64.

Families: 'The last to know'

The play is structured around three of eight mothers Slovo met at a community centre in Molenbeek - months before the town became significant for its association with the Paris and Brussels attacks.

"All their children had gone to Syria at various stages and they [the mothers] had come together to support each other, but also to try and warn other parents of the signs of what is happening to your kid because all of [the families] were taken by complete surprise," Slovo said.

We hear the women's tragic stories: One's son was killed in a bombing raid in Syria, another's son blew himself up outside a football stadium in Paris, and the last woman's daughter is believed to still be in Syria.

Slovo believes ISIL attracts young people who don't have enough to lose, who are looking for a sense of identity, who experience racism or Islamophobia, or feel pressure from friends.

"The mothers just showed me how difficult it is to be a mother in that situation because even if you know all these things, you still blame yourself. That is what Islamic State has done to them," Slovo said.

Most - but not all - families are often the last to know; then, in their grief, they face recriminations from society for their child's actions.

The play also looks at the UK government's counter-radicalisation Prevent strategy which requires doctors, social workers and teachers to report anyone they believe may be thinking about joining ISIL.

"The play is not meant to be just about why these kids went, because there are hundreds of reasons why kids can go. But it was also about what our response should be," Slovo said.

In the words of four teenage students from East London, we hear that the strategy is flawed, and Slovo believes it could be making things worse.

"If Muslim kids feel they can't express themselves, it's very worrying for us because people need to talk about things in order to have their minds changed," Slovo said. "If you drive it underground, it's dangerous. There's no teacher who can argue with them .... There is nobody in authority for them to talk with."

One young man says he's exactly the same as his fellow British citizens, with all the same fears.

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"He thinks people look at him and think, 'Oh, you're Muslim and you're not even scared by this.' But he too worries that if he goes into the Underground [subway system] he's going to be blown up because Islamic State does not distinguish," Slovo said.

The young people say they are stared at on the Underground, heckled to go back to where they've come from, and are worried about the rise of Islamophobia.

Still, Slovo believes the UK's commitment to multiculturalism means integration is comparatively better here.

"It was so absolutely clear in Brussels and absolutely clear in France that feelings of exclusion by those kids is one of the biggest driving factors over there," she said.

'Damaged people create damage'

Slovo is in a unique position to delve into identity and integration. Britain is her adopted country. She was born in South Africa where her parents, Joe Slovo and Ruth First, were committed anti-apartheid activists. In 1982, the South African security forces assassinated her mother.

The play gives an explanation of the goals of ISIL through the words of Abu Bakr al-Baghdadi, the group's leader. An analysis of the chances of eliminating the group in Syria and Iraq is offered by Charlie Winter, an expert from Georgia State University.

Slovo said young people grow up: They settle down, have kids, and stop rebelling against their parents. But there is a constant supply of young people - many looking for some meaning in their lives - who become prime targets for ISIL recruitment.

Also in the play, we hear the words of the Reverend Paul Fitzpatrick, who says ISIL recruiters make sure their fliers are underneath other pamphlets and posters on a busy bulletin board. The recruiters are looking for those who are willing to spend time going through all of the leaflets for events and advertisements - those with holes in their lives.

Slovo asked Fitzpatrick if people who had gone to Syria should be allowed back into the country. He replied: "Of course they should come back - because they are British citizens.

"But you have to pour so much resources into them," he added. "Not necessarily to track them to see if they're doing anything wrong, but because they will have been damaged, and damaged people create damage."