Oxford couple John and Sally Letts reject claims son Jack - dubbed 'Jihadi Jack' - has joined so-called IS and urge him to return home

John and Sally Letts, of Grandpont said they felt "betrayed" by claims their son had become a fighter for the terrorist group, describing him as "kind, funny, and gentle".

Jack Letts, 20, remains in contact with them via social media. He is believed to be in Syria but has repeatedly assured them he is not a member of Islamic State.

He criticised media reports claiming he had adopted an Islamic name – Ibrahim – and had a son, writing on Facebook they "got bored worrying about what colour socks certain celebrities wear and took out their frustration on me".

• Jack Letts in a picture he posted in May 2015 at the Tabqa Dam on the Euphrates, 25 miles outside Raqqa in Syria

Mr and Mrs Letts said Jack told them he wanted to travel to Syria for humanitarian reasons.

They said: "The things that have been written about him are completely false. The police and security services say they have no evidence he has done anything wrong.

"We monitor Jack's social media accounts every single day and he has never posted photographs of weapons.

"He is a really kind, funny kid who is very gentle.

"He is totally non-violent and was only motivated by one thing: every day, on the television and computer screens, there were constant pictures of Syria, and the hundreds dying and starving or being bombed by Assad.

"Jack was totally disturbed by that. He is a very humane person and he wanted to do something to help.

"We last saw him just under two years ago and we have been living in hell ever since.

"Now we just want him to come home. But failing that, we want him to be in a safe country."

Mr Letts added: "I feel like my son is walking on a railway track, blindfolded, and there's a train coming and he can't hear me, like I can't do anything about it.

"It has been a nightmare."

Jack grew up in Oxford, playing football for Northway Boys under-10s and attending Cherwell School before he later converted to Islam.

His former football coach, Steve Carter, said: "Jack was just one of the boys."

It emerged yesterday he had travelled to Kuwait in the summer of 2014 to learn Arabic, before reportedly travelling to Syria in September 2014.

Mr Letts, an archaeological botanist, said his son had become interested in Islam at 16 and had sought to be "the best Muslim possible", visiting most of the city's mosques and seeking out different groups for religious discussions.

He decided to study Arabic in Kuwait after becoming increasingly concerned about the conflict in Syria. Three months later he left, and his parents believe he is now in the civil war-torn country, possibly working in hospitals or as a translator.

Mr Letts said: "He said he wanted to help in refugee camps and so I said, 'you'll be useless unless you learn Arabic.'.

"So he said, 'OK, I'm going to learn Arabic.'.

"As a parent, what can you do? Lock your child in their bedroom? What we tried to do was positively channel his interests.

"Jack is a clever kid. He was reading a lot and believed he had to consider all the different opinions before making one himself.

"We were both raised as Christians but we are a secular household. We didn't oppose his conversion.

"We live in a democracy and if he wants to believe something and he is not hurting anyone else then that is fine. That is how he was raised."

It is believed more than 750 British men and women have travelled to Syria and Iraq to fight in the civil war. Mr Letts added: "There are hundreds of parents in this same situation."

Oxford Imam Dr Hojjat Ramzy yesterday said Jack had first come to Oxford Islamic Information Centre, in Saint Omer Road, about three years ago to be taught about Islam.

He added: "I knew Jack really well, he is a very good person. He was kind and very pious and used to come and sit and learn.

"I am very sad he has gone out there, if I had known before I would have talked to him and I hope he would have reconsidered going.

"Young people come and ask me ‘should we go to Syria?’ and I prevent them. We want peace in Syria, we don’t want killing there.

"We want people to be sensible and rational and if you have any difficulties then come to us and we can explain what true Islam really is."

Dr Ramzy said Jack later began to associate with lots of different Muslim groups and he did not see him again.

A spokesman for the Foreign Office refused to comment on Jack Letts but added yesterday: "The UK has advised for some time against all travel to Syria.

"As all UK consular services there are suspended, it is extremely difficult to confirm the status and whereabouts of British Nationals in Syria.

"Anyone who does travel to these areas, for whatever reason, is putting themselves in considerable danger."