Indonesians returning from life in Islamic State's rapidly-shrinking caliphate have described a horrific and brutal world — a "pit of lies" where fighters chased three things: power, money and women.

Key points: The Muslims say they were enticed to the IS caliphate by promises of a better life

The Muslims say they were enticed to the IS caliphate by promises of a better life The returnees describe IS members' greed, violence and mistreatment of women

The returnees describe IS members' greed, violence and mistreatment of women Indonesian authorities are using returnees' testimonials in a video fighting extremism

The Indonesians feature in a video released by the nation's anti-terror body, the BNPT.

They are devout Muslims who say they were enticed to life in the IS caliphate by promises of a better life. The Indonesian Government says they did not go to fight — but to become willing citizens of what they thought was a holier place.

What they found was awful.

"Their promises are all empty," one woman, Lasmiati, said.

Lasmiati says Islamic State's promises are empty. ( Supplied: BNPT )

"It's tough there," said another, Difansa.

"For people who haven't gone there, be grateful for not falling into the crocodile's lair, it's a pit of lies.

"Save your time, save your money, save your life. Don't waste your life only to get lied by ISIS.

"ISIS will be destroyed soon if God is willing.

"I believe ISIS will be destroyed soon, their purpose is not to enforce God's words, God hates them."

These are extraordinarily blunt comments from a group of people who were once IS's most enthusiastic supporters.

They are deeply religious people brought up to believe an Islamic caliphate is the ideal place in which to live.

"Just because it's a caliphate, it doesn't mean all will be good," one woman, Naila, said.

"I never thought it would be that bad after I entered Syria. When I arrived at the women's dorm, their behaviour, oh my God, I can say it's worse than animals."

Woman describes 'jihad marriage'

The returnees are not in custody in Indonesia because they have not broken local laws.

An estimated 800 Indonesians are thought to have travelled to Iraq and Syria to live in the caliphate.

Some, like Difansa, brought their children with them. She was shocked by the greed of the fighters.

"ISIS are after three things: power, money, and women," Difansa said.

"When it comes to women, it is very clear, I saw it myself. When me and my family arrived, the members of my family who were single were chased after.

"They call it jihad marriage, and for the people there, getting married is like a competition.

"They get married once, twice, until the fourth time then divorce again, married again. I don't know how many times already — and it is facilitated by ISIS.

"Every person who marries a virgin gets money from ISIS."

Heru says people were assaulted if they made mistakes during religious study. ( Supplied: BNPT )

One man, Heru, described watching children kick a decapitated head around the streets.

"It was midday, I was wondering what was the crowd doing at the clocktower. When I got closer, I thought ' oh my God, they play with dead people'".

Even religious study was a nightmare, Heru said.

"I was so stressed. We were afraid there. If we made mistakes we were hit," he said.

"There were six of us Indonesians with one teacher. We took turns reading the Koran and when it was my friend's turn to read there was a mistake.

"After repeatedly making the same mistake, the back of his head was hit. I was there, his ears were pulled and they screamed in his ear how the verse should be read.

"I was angry but I couldn't do anything. But when I remember, I'm sad I couldn't do anything, to see him treated like that, he was crying, as loud as he can."

Indonesian authorities hope the video serves to counter the messages of paradise and harmony delivered in IS's slick online propaganda.