In the latest five-minute video, Cantlie warns that the United States and its allies are embarking on "Gulf War III", adding "Not since Vietnam have we witnessed such a potential mess in the making".
    
"Current estimates of 15,000 troops needed to fight the Islamic State are laughably low. The State has more mujahideen than this. And this is not some undisciplined outfit with a few Kalashnikovs," Cantlie said in the video.
    
Dressed in orange against a backdrop showing cuttings from the 'New York Times', the 43-year-old freelance photojournalist introduces himself as "the British citizen abandoned by my government and long-term prisoner of the Islamic State".
    
The video follows the similar pattern to the first video featuring the journalist and is introduced with the title "Lend Me Your Ears" and "Messages From The British Detainee John Cantlie".
    
He describes the IS as the "most powerful jihadist movement seen in recent history" and that the US led group could not harm it.
    
The IS, which now controls roughly a third of Syria and Iraq, has beheaded two US journalists - James Foley and Steven Sotloff and a British aid worker - David Haines, as they have threatened to kill another British captive named Alan Henning.
    
Cantlie, who in July 2012 escaped an earlier kidnapping in Syria, returned to the country towards the end of 2012 and got kidnapped second time by the extremists.
    
His whereabouts are not known but it is likely that Cantlie is being held in Syria where other hostages were beheaded.
    
This latest clip has been circulated as the US and its allies launch air strikes against IS in Syria. UK forces are not involved but the government says it has not ruled itself out.

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