The mother of one of the young men who appeared in a in a recruitment video for the terrorist group Islamic State in Iraq and the Levant (Isis) has made an emotional appeal for him to come home saying he had been "brainwashed".

Reyaad Khan appeared in the video alongside Nasser Muthana and one other Briton calling for other westerners to join them fighting in Syria and claiming they were going to join the war in Iraq, where the army is struggling to repel the Sunni insurgents.

On Sunday, Khan's mother, speaking from Cardiff where the family live, said they had been devastated when the video appeared.

"I was absolutely shocked to see how his character has changed," she said. "They are being brainwashed into thinking they are going to help people – I don't know who is doing this but there is someone behind them. These are young innocent boys who are being brainwashed."

In the interview broadcast on Sky News she said Khan was a "lovely kid and son and brother … He was the most lovely boy any mother could have he was always there for his family."

In an emotional appeal directly to the 20-year-old, she could not eat or sleep until her son returned.

"Reyaad please come back, I am dying for you, you are my only son. It is not good what you are doing … you are going to regret this for the rest of your life."

Khan and Muthana, both 20 years old, appeared alongside a third man with a British accent and two Australians in the video – entitled There's No Life Without Jihad. They are seen holding guns surrounded by greenery as they implore others to join them.

On Sunday it emerged that Khan and Muthana were both from Cardiff and attended the same sixth form college. Khan's Facebook page shows a boy with typical concern and interests from sport to his mother's nagging. In 2010 he wrote he wanted to become the first Asian prime minister. But in more recent entries he regularly refers to the plight of the Syrian people and how the conflict is being misrepresented in the west. He goes on to say how people all over the world are "answering the call" to join the fighting.