FILE - In this March 14, 2015 file photo, Iraqi Shiite militia group called Imam Ali Brigades chant slogans against the Islamic State group at the battlefield in Tikrit, 130 kilometers (80 miles) north of Baghdad, Iraq. From Lebanon and Syria to Iraq, Yemen, and the Gaza Strip, Iran has significantly expanded its footprint over the past decade, finding and developing powerful allies in conflict-ravaged countries across the Middle East. Iran has trained, financed, and equipped Shiite militias in Iraq that battled U.S. forces in the years after the 2003 invasion and remobilized to battle the Islamic State group a decade later. (AP Photo/Khalid Mohammed, File)
Iraqi Shiite militia group called Imam Ali Brigades chant slogans against ISIS on a battlefield in Tikrit, 130 kilometres north of Baghdad. AP, file

US-Iranian escalation tests Tehran's militias in Iraq