WASHINGTON (AFP) - A French fighter for the Islamic State in Iraq and Syria (ISIS) painted life in the so-called caliphate as a civilised place, in a video posted by the extremist group Saturday.

ISIS said the narrative of the approximately 65-year-old former army trainer and businessman it dubbed as Abu Suhayb al-Faransi marked the first episode of a new series, according to the US-based Site monitoring network.

Faransi, sporting a henna-tainted beard, military fatigues and tainted glasses, spoke in the 15-minute video about his conversion to Islam, his pursuit of jihad and rejection of the Nusra Front, Al-Qaeda's branch in Syria.

Faransi recalled IS supremo Abu Bakr al-Baghdadi's announcement in June that the fighters were establishing a "caliphate" straddling large chunks of Iraq and Syria.

"From then on, I told myself there was no doubt, I had to join," the Frenchman said.

He recalled having initially a "distorted view" that the group was extremist, but found the opposite was true when he came to territories under its control.

"When I entered the land of the caliphate, I saw that there were different things, institutions, cleanliness, engineers, doctors, sensible people, people who left Europe, who left other lands from across the world to knowingly come fight jihad completely honestly," the man said.

Faransi said "the law of Allah," or syariah, was being applied in the caliphate.

"This is one of the reasons why I joined the Islamic State. We are completely safe here, despite the bombings, the drones and the MiGs (Russian warplanes)," he said.

"Nothing will halt the advance of the Islamic State."

ISIS, which conquered nearly a third of Iraq virtually unopposed nine months ago, has built a reputation for violence by beheading and crucifying its victims in public or on tape.

But Iraq's allies, led by the United States and Iran, have since helped organise a major counteroffensive that is steadily shrinking the group's footprint.