A video has emerged believed to show ISIS executioner Jihadi John ranting on camera shortly after he arrived in Syria from the UK. The footage is of two bands of fanatical fighters joining forces in 2013 under the command of notorious terrorist Omar al-Shishani. At the front stands a man thought to be Mohammed Emwazi - the west Londoner last week unmasked as the killer of Western hostages in a series of videos which have shocked the world. A man thought to be Jihadi John proclaims allegiance to a terror group in footage filmed in 2013. The video is thought to be the first known appearance by the executioner now unmasked as Mohammed Emwazi . The video is thought to have been filmed  just months after Emwazi is understood to have fled Britain to take up arms alongside the extremists. It shows a pledge of allegiance made when the so-called 'Army of Muhammad Brigades' group joined forces with the so-called 'Brigade of Migrants', of which Emwazi is believed to have been a member. The speaker proclaims: 'This army announces unity within its ranks for the sake of implementing the Shariah and returning this blessed land to God the most glorified and the most high under the leadership of the emir Umar al-Shishani.' Emwazi, now 26, attempted to join al-Shabaab in Somalia after finishing his university course in London in 2009, but was refused entry to Tanzania and  returned to Britain, from where he later went to Syria. He is thought to have been in a group who were among the first to go to fight in the Middle East, along with fellow Londoners Ibrahim al-Mazwagi, Choukri Ellekhlifi and Mohammad el-Araj. Ellekhlifi was two years above Emwazi in his north London school, Quinton Kynaston Academy, and later became part of a robbery gang which carried out a series of raids in central London. Ellekhlifi, 22, fled to Syria while on bail and was killed fighting near Aleppo in August 2013, months after the video thought to feature Emwazi was filmed. El-Araj, 23, was killed two weeks later during a firefight. Al-Mazwagi, from North London was 21 when he was killed in Syria in February last year. Emwazi was last week unmasked as the killer who carried as series of beheadings of Western hostages . In the film, the man thought to be Emwazi stands in front of notorious terror leader Omar al-Shishani (right) Emwazi's links to the London crime gang meant he had developed a love of violence, which led to him being chosen to feature in the beheading videos for which is now known throughout the world. In the latest video, the man suspected of being Emwazi stands at the front of a long line of gun-toting militants, with al-Shishani standing behind him arm-in-arm with two other fighters. Commenting on the likenesses of Emwazi to the speaking in the latest video to emerge, Raffaello Pantucci of the Royal United Service Institute told MailOnline: 'Given he’s masked, it is difficult to make the precise connection between the two, though there are definite similarities. 'Given the group and community that Emwazi came from – the West London group - were all alongside the Katiba al Muhajireen under Omar al Shishani, it might well fit that it could be Emwazi. 'Given his solid Arabic and his willingness to be front and centre in films, it would fit that it could be him. Al Shishani seems to have been quite willing to record films of himself with his foreign fighter warriors.' Charles Winter from the Quilliam Foundation added: 'There are certainly similarities between Emwazi and the man speaking in this video, the eyebrows for example. 'In terms of the group, we know that it has a large proportion of foreign fighters so there's a possibility that he could have joined but I'm unable to say whether it is definitely him. The video shows a pledge of allegiance to Omar al-Shishani, now a commander of ISIS in Syria . Emwazi is thought to a fighter (second right beneath flag) who appears in another photo featuring al-Shishani . Mr Winter added: 'While he does have certain features that resemble Emwazi, there have been numerous false alarms with ID-ing "Jihadi John" in the past. A balaclava does a lot to obscure one's face, and a lot to make people look similar, too.' Others have cast doubt on whether the man is Emwazi, saying the speaker in the film looks shorter than the Londoner and appears to be holding the Kalashnikov rifle with his right hand, whereas Jihadi John held his knife in his left hand. If the video does show Emwazi, the footage would be the first known time he appeared on camera in Syria after going to fight. It is believed he was one of more than 700 fighters in The Migrants Brigade who arrived in the Middle East three years ago. The group were not part of ISIS at the time the video was filmed, but joined the group in the months that followed. Emwazi has since become one the world's most wanted men after he appeared in a series of gruesome videos beheading a series of foreign hostages, including British aid workers Alan Henning and David Haines and US journalists James Foley and Steven Sotloff. Mohammed Emwazi is believed to have among a group of Brits, which also includes Ibrahim al-Mazwagi (left), Choukri Ellekhlifi (centre) and Mohammad el-Araj (right), who were among the first to travel to Syria to fight . Ibrahim al-Mazwagi (centre), the first British jihadi known to have died in Syria, is pictured here with Abu Omar al-Shishani (right), one of the most feared military commanders of the Islamic State of Syria and Iraq . Omar al-Shishani has  moved from the conflicts of the Caucasus, south of Russia to become one of the most feared commanders in the ISIS army now terrorising Syria and Iraq . Omar al-Shishani, whose real name is Tarkhan Batirashvili, is an ethnic Chechen from the Caucasus nation of Georgia, specifically from the Pankisi Valley, a centre of Georgia's Chechen community and once a stronghold for militants. He fought in the brief conflict between Russia and Georgia in 2008 and became a jihadist after being discharged from the Georgian military on health grounds after contracting tuberculosis. After recuperating and being refused re-enlistment, he was arrested for stockpiling weapons and jailed in September 2010. Following his release, he travelled to Istanbul in Turkey in March 2012 to join Chechen rebels in the Syrian conflict. The red-bearded fanatic became the commander of the Brigade of Migrants, which was initially aligned with al-Qaeda's Jabhat al-Nusra. The group merged with other jihadists in March 2013 to form the Army of Emigrants and Supporters, a larger and more structured group with a religious council. In May 2013, Shishani switched to supporting the Islamic State of Iraq and Syria and has become the group's military commander in Syria, leading it on an offensive to take over a broad stretch of territory leading to the Iraq border. Numerous reports of his death since then are thought to be untrue.
Video shows two bands of militants joining forces during Syrian war . Jihadi John believed to have been member of one of the groups involved . Man who looks like British-raised ISIS execution makes proclamation . Experts highlight similarities between speaker and Jihadi John . He swears allegiance to group run by notorious terrorist Omar al-Shishani . Al-Shishani also appears in the footage, arm-in-arm with other fighters .