Reports have surfaced of disagreements between Iraqi and American officials over an ongoing offensive against the Islamic State.

According to the New York Times, American officials and Iraqi government leaders are conflicted over the timetable of the offensive against ISIS in Mosul, as well as the prominent role that Iran is playing in the current battle to reclaim Tikrit.

American personnel told the newspaper that there are Shiite militias connected with Iran that are now fighting alongside the Kurdish fighters and Iraqi army elements. Iranian Major General Qassim Suleimani is also reportedly leading the Shiite militias near the frontlines.

The NY Times said that American leaders are concerned that the participation of Shiite militias could further inflame the sectarian divide between Shi'a and Sunni Muslims that ISIS took full advantage of as it swept through the country.

Iraqi officials are also reportedly frustrated at what they describe as the "sluggish" pace at which the US is conducting its efforts to liberate Mosul and the Western Iraqi province of Anbar from the Islamic State.

It was previously announced that a major offensive to reclaim Mosul from the ISIS will begin in April or May. However, the Wall Street Journal (WSJ) reported last week that the US has altered its timetable for the attack. Instead, it is mulling over months of sustained airstrikes against Islamic State positions in and around Mosul before sending in Iraqi ground forces.

"When we feel that the Iraqi forces are ready to go and win decisively, we will go and advise the Iraqis to begin the operation," a military official was quoted by the WSJ as saying. 

That has not gone down well with the Iraqi government. 

 "The Americans continue procrastinating about the time it will take to liberate the country," Ali al-Alaa, a close aide to Prime Minister Haider al-Abadi, told the NY Times in an interview. "Iraq will liberate Mosul and Anbar without them."