The distraught man, who has not seen his son for three years, said the boy (pictured) was 'brainwashed' by his mother, Sally Jones

The father of a young boy taken to Syria by his British mother has spoken of his shock at seeing a video which apparently shows his son executing a captured prisoner.

The distraught man, who has not seen his son for three years, said the boy was 'brainwashed' by his mother, Sally Jones, after being taken by her to join Islamic State.

The 47-year-old mother of two, from Chatham, Kent, was declared one of the world's most wanted terrorists by the UN after she fled to Syria with her youngest son JoJo, then aged 10, in 2013.

Now the father believes it may be his son in a chilling propaganda video released on Friday showing five boys murdering a group of captured Kurdish fighters.

Last night the man, who has asked not to be named to protect his safety, said: 'He was brilliant, just a normal boy – always chasing bugs, going down the park. I have had to block it out. It's been hard, we just have to carry on. It's disgusting he's been brainwashed.'

Jones gave birth to JoJo in Kent in 2004 but split from his father shortly afterwards. She then converted to Islam.

A friend of the father said: 'Sally would send him texts that were disgusting. She would threaten to take JoJo to Islamic rallies and leave him there. It was awful.'

Jones gave birth to JoJo (second right holding weapon) in Kent in 2004 but split from his father shortly afterwards. She then converted to Islam

After their split, Jones married an Islamic radical 25 years her junior, changed JoJo's name to Hamza, and the three of them fled to Syria.

In the latest sickening nine-minute Islamic State video, the boy is called Abu Abdullah al-Britani. Al-Britani is a nom-de-guerre often used by terrorists from Britain.

The other children are captioned as being from Egypt, Kurdistan, Tunisia and Uzbekistan.

Wearing military fatigues and black bandanas, the boys point their handguns in the air before aiming them at the back of the heads of the captured hostages and firing.

The friend of the father added: 'He was a happy boy, loving, caring, sensitive and a pleasure to be around. I'm angry at Sally for taking an innocent child who doesn't know right or wrong. Children can be easily manipulated.

'He's an innocent party and I want to know what makes a mother put her child in such a dangerous position.' According to the Quilliam Foundation anti-extremist organisation there are about 50 British-born children living in areas under IS control, although very few of them are believed to be white.

Jihadi bride Sally Jones, pictured here in December 2004, fled the UK in 2014 along with her son JoJo, pictured here just days after his birth, where the pair converted to Islam

After their split, Jones (pictured) married an Islamic radical 25 years her junior, changed JoJo's name to Hamza, and the three of them fled to Syria

Jones played guitar in an all-girl rock band called Krunch in her 20s and had a boy, Jonathan, in her 30s.

But according to neighbours, after the boy's father committed suicide, Jones moved into a two-bedroom terraced council house in Chatham, Kent. Neighbours said she had a series of transient relationships and became addicted to drugs.

In 2013, she married Junaid Hussain, an Islamic radical and hacker 25 years her junior, and they took JoJo with them to Syria. He was killed in a US drone strike last year.

In the months that followed, she posted chilling threats on social networking sites and posed for photos with an AK-47, dressed in black with her face veiled.

Using the pseudonym Umm Hussain al-Britani, she said she wanted to behead Christians with a 'blunt knife' and praised Osama Bin Laden.

The Foreign Office said it was aware of the video but was unable to comment further.