Jihadist Nasser Muthana's home-made bomb pictures
Pictures of home-made bombs have been posted on a social media account by a person claiming to be one of the three men from Cardiff who have joined a Jihadist group in Syria.
The man claiming to be Nasser Muthana, 20, used an unverified social media account to show the devices in Syria.
"So the UK is afraid I come back with the skills I've gained," he stated.
It comes after a person claiming to be Nasser's brother Aseel told BBC Wales he was willing to die for the cause.
The 17-year-old, who is also believed to be in Syria, told the Week in Week Out programme: "Jihad is obligatory."
Nasser and another man from Cardiff, Reyaad Khan, 20, appeared online two weeks ago with a man from Aberdeen in a video apparently filmed in Syria urging others to join Isis (Islamic State in Iraq and the Levant).
Now in a social media account, a man believed to be Nasser has posted a photograph which appears to show around 15 home-made bombs packed inside metal containers.
He also posted a photograph showing a home-made weapon said to be taken from an 'enemy' Shia Muslim.
The brothers' father Ahmed Muthana, 57, said this was "not the son I know", adding he wanted his children to come home even if they were imprisoned on their return.
He said: "What they are doing or posting online, they are being told to by the people with the guns who feed them, look after them and have control over them.
"I think they are trapped in the situation and that makes it hard for them to come back or leave the place."
He said he had not had any contact with either of his sons since they left.
Meanwhile, an 18-year-old arrested on suspicion of terrorism offences which may be linked with the Cardiff Jihadists has been bailed.
South Wales Police said on Wednesday evening that a Grangetown man had been questioned over claims of assisting in the preparation of an act of terrorism.
Police confirmed they were investigating a possible connection with the Jihadists in the video.