ISIS is urging its fighters in Syria to move to the front-lines of its battle in Iraq, where the extremist organization has been losing intense battles against Iraqi security forces, according to documents obtained by Syrian groups fighting the terrorists.

“The crusader, the Shiites and the apostate Arabs are storming our brothers in the provinces of Anbar and Salahedine,” the ISIS document says, referring to heavy fighting in Iraq. In the statement, which was obtained by anti-ISIS fighters in Syria and could not be otherwise authenticated, extremists wanting to join the fight in Iraq should register at mosques in Manbaj, a town near Aleppo.

ISIS has sustained intense fighting for terrain previously captured in the northern Iraqi city of Tikrit and most recently in the western province of Anbar and the city of Ramadi. ISIS launched another siege against the city about two weeks ago. […]