The influence of Iran in Baghdad’s largest offensive against the jihadist group Islamic State in Iraq and Syria (Isis) raises concerns about the government’s ability to coordinate a strategy to retake northern Iraq.

Iraq’s assault on the Tikrit area involves at least 20,000 fighters including the Iraq Security Forces (ISF), Shia militias and Sunni tribal forces. But the Iran-backed Shia militias dominate the numbers in the Tikrit assault force, while the commander of the Iranian Revolutionary Guard’s Quds Force, Qassim Suleimani, is reported to be overseeing the eastern part of the offensive.

The strong presence of Shia militia increases fears of escalating sectarian violence in Sunni-majority Tikrit and the surrounding Salahuddin province. Shia militia leaders have denied accusations of mass killings and theft after previous victories against Isis in Sunni areas.

Retaking Tikrit will be an important test of Baghdad’s capabilities for its final goal of retaking Mosul – Iraq’s second-largest city and a key Isis stronghold in northern Iraq.

“The ISF will need to develop a coherent strategy from what appear to be separate developing plans to clear Isis from Salahuddin, Anbar and Ninevah,” says Sinan Adnan, analyst at the Washington-based think-tank Institute for the Study of War.

“The development of disconnected strategies for these areas does not bode well for a unified effort to defeat Isis in Iraq,” he adds.

Baghdad began the assault by targeting two areas east and south of the city – Alam and Dour – both Isis strongholds that can be used to launch attacks in the surrounding areas. The forces, which have been delayed by bombs and sniper fire, have yet to move into the centre of Tikrit, according to reports.

The Tikrit offensive is not directly backed by the US-led international coalition, which has been providing the ISF and the Kurdistan Regional Government’s (KRG’s) forces support in the fight against Isis further north.

An official from the US military’s Central Command revealed in February plans for a US-backed operation to retake Mosul, which the Pentagon has since admitted was a mistake.

What remains to be seen is whether Washington and its Western allies can work on the ground with forces commanded by Iran’s Revolutionary Guards.

In Washington, the Quds Force is considered a banned terrorist organisation responsible for supporting Shia paramilitary forces across the Middle East.

Even a positive outcome to the ongoing nuclear negotiations between Washington and Tehran is unlikely to see their respective militaries openly sharing strategies to fight Isis.