The child appeared with four others in gory propaganda footage released last month that showed him shooting a kneeling prisoner in the head while wearing combat fatigues.
The Twitter account claiming to belong to Sally Jones, a British jihadi bride
Jones took Joe “JoJo” Dixon to Syria when she fled the UK to join the so-called Islamic State in 2013, when he was just eight or nine years old.
His father, who remained anonymous over fears for his safety, has not seen the boy since but told the Mail on Sunday he thought the child in the video may be his son.
“He was brilliant, just a normal boy – always chasing bugs, going down the park,” he said. “It's disgusting he's been brainwashed.”
Joe’s grandparents are also reported to have recognised him in the video, although there has been no official confirmation of the child’s identity.
On Saturday, a person claiming to be Jones sent out a series of messages on Twitter denying the reports and issuing a stream of threats towards the UK for its air strikes against Isis.
“Its not my son,” the messages said. “If it was my son in the video i would be very proud, and may Allah swt [glory to him, the exalted] reward all of them cubs of the khilafah [caliphate] aameen.
“By the way my son collects grenades now...not bugs Alhamdulillah for getting my beautiful boy to the Islamic State [all sic].”
Timeline: The emergence of Isis
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The Twitter account used the name “Mrs Terror” and handle "Mrs Hussain", referring to Jones’ former husband Junaid Hussain, a British jihadist who was killed in a US drone strike last year.
The origin of the Twitter messages could not be verified but their style and rhetoric matched previous accounts operated by Jones, using the same profile picture of a crying Statue of Liberty.
The accounts frequently shut down by Twitter before re-appearing with a new handle to evade detection by authorities.
The latest account gave Jones’ location as Isis’ de-facto Iraqi capital of Mosul. She is believed to have previously lived with her son in the Syrian city of Raqqa.
It included a photo of two guns, one smaller than the other, with an emoticon of a love heart and the caption: “Our AK47s <3”.
The person posing as Jones wrote that their day had been “disturbed” by media reports, forcing them to reappear on Twitter to correct them.
Children at an Isis training camp for its 'cubs of the Caliphate'
They called the boy in the execution video a “cub of the Caliphate” – a name used by Isis to describe boys brainwashed and trained as child soldiers in camps.
The other children in the footage were captioned with names showing them to be from Egypt, Kurdistan, Tunisia and Uzbekistan.
Europol warned earlier this year that Isis was training boys born to foreign fighters across its territories in Iraq and Syria to be the “next generation” of terrorists.
The group advertises its use of children as fighters and suicide bombers, and may also be planning to use them for recruitment and radicalisation abroad, experts said.
More than 50 children from the UK are living in the “caliphate”, where there are also an estimated 31,000 pregnant women, an investigation by the Quilliam Foundation found earlier this year.
Among them is Isa Dare, the son of a London woman known as Khadijah Dare, who was shown appearing to blow up a car containing three prisoners in a propaganda video in February.
“We will kill the kuffars (infidels) over there,” he was shown saying, while wearing military fatigues and an Isis headband, almost four years after being taken to Syria as a baby.
Isa Dare appearing in an Isis propaganda video
The whereabouts and role of Jones’ son, who would now be aged around 12, is unclear but boys of his age are routinely conscripted for terror training in the group’s territories.
Jones, 47, travelled from the UK to Syria in 2013 to marry Hussain and join the so-called Islamic State.
The couple targeted American military personnel through publication of a “hit list” online to encourage lone wolf attacks and Jones became prolific for her social media use.
While issuing public calls for attacks in the UK and giving instructions for constructing homemade bombs, she has used social media to recruit women to join Isis.
In September last year, Jones was sanctioned as an agent of terror by the United Nations, putting her under an assets freeze, travel ban and arms embargo. She has also been listed as a terrorist by the UK and US.
Using the name Umm Hussain al-Britani, Jones has declared her wish to behead Christians with a “blunt knife” and threatened attacks in British cities and on the London Underground.
Before converting to Islam and joining Isis, Jones lived in Kent on welfare payments and played guitar in a punk rock band, with interests in conspiracy theories and witchcraft.
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