David Petraeus, who commanded US troops in Iraq during 2007-2008, has voiced concerns over reports of sectarian atrocities committed by the Shia Popular Mobilization Units (al-Hashd al-Sha'bi or PMUs) as well as by Iraqi security forces.
Around 60,000 Iraqi soldiers supported by Kurdish Peshmerga forces and Popular Mobilization Units are fighting against roughly 4,000 ISIS militants.
The government forces include largely Shiite Muslim militias known as Popular Mobilization Units.
Last month, an improvised explosive device killed a leader of Iraq's Hashd al-Shaabi, or the "Popular Mobilization Units" (PMU), in the Sunni majority town of Gharma.
Dempsey said the forces advancing on Tikrit were overwhelmingly composed of 20,000 Iranian-backed Shi'ite Muslim militias known as Hashid Shaabi (Popular Mobilization) units.
Members of the Iraqi paramilitary Popular Mobilization units, which are dominated by Iran-backed Shiite militias, celebrate after regaining control of the village of Albu Ajil from the Islamic State group on March 9 , 2015
The source said Abadi has added "cosmetic touches" on the Shia Popular Mobilization Units, by giving them the Iraqi flag and saying their participation in the battle will be in the rear lines.
The source believes the Gulf sees Abadi as a weak man who is not able to rein in the Popular Mobilization Units run by former PM Nouri al-Maliki, and Iran's Revolutionary Guards not far behind him.
Although the Shiite militias, known as Popular Mobilization Units, spearheaded the Tikrit offensive, many Sunni officials were wary of their participation in Anbar, especially after allegations of sectarian-driven abuses by militiamen against Tikrit's Sunni population.
The Popular Mobilization Units spearheaded a successful government offensive in March to rout Islamic State from the central province of Salahuddin, but the militiamen were not initially deployed in strength in Anbar because of sectarian sensitivity.
