Dressed in orange jumpsuits - attire usually worn by ISIS's victims - the Jaysh Al-Islam soldiers lead 13 shackled jihadis to their deaths.

Jaysh Al-Islam calls itself the 'Army of Islam' and reportedly commands as many as 25,000 loyal fighters following the merger of around 60 rebel factions inside Syria.

Islamic State's captured soldiers are forced to kneel as a commander announces: 'Allah did not make a disease without appointing a remedy to it.'

The jihadis - dressed entirely in black - are then given something to drink before each of their faces are clearly shown in the 19 minute-long propaganda video. They are then shot in the back of the head at point blank range with shotguns.

Before they are killed, a Jaysh Al-Islam militant says: 'The most serious calamity for our jihad today is a group of people who grow at a time of division among Muslims.

'This group claimed to be the mother state and made Takfir [accused of apostasy] on other Muslims, shed their blood and looted their properties and dignities.

'They worsened... the ordeal of Muslims by corrupting their religion and livelihood and killing the jihadi leaders who did their best to help our stricken nation.

'They wreaked havoc on our people in liberated areas and cut the supply route of jihadis. They left... Tehran intact and instead they attacked our mosques.

'This is the penalty for what they have committed. We also call on their fellows to repent.'

In April this year, Jaysh Al-Islam released a striking video showing off 1,700 troops, a fleet of armoured tanks and special forces soldiers in an impressive military parade.

It operates in the war-ravaged Syrian city of Damascus and its ongoing battle against President Bashar Al-Assad is reportedly funded by the wealthy nation of Saudi Arabia.

The Arab kingdom has sent millions of dollars to arm and train their fighters so they can defeat the Syrian regime and 'increasingly powerful Jihadi organisations', according to the Guardian.

Known as the Army of Islam, the insurgent group was created in 2011 when Saudi Arabia allegedly engineered the merger of over 50 rebel factions after growing alarmed at the rise if Al-Qaeda and ISIS in Syria.

It is a fierce enemy of both those Islamist groups as well as Jabhat Al-Nusra, but embraces independent rebel forces and 'non-Jihadi' units. 

Their graduation ceremony for trainee soldiers in the Ghouta suburb of Damascus was attended by the militants' leadership who watch proudly as their troops march in perfect unison across the expanse.

Jaysh Al-Islam is led by Sheikh Zahran Aloush who addresses the thousands of armed soldiers and tanks once they have assembled on the vast concrete ground below.

(dailymail.co.uk)