Air strikes by the US-led coalition would help win the battle to retake the Iraqi city of Tikrit from the Islamic State of Iraq and the Levant (ISIL), one of the operation's commanders has said.

Staff Lieutenant General Abdulwahab al-Saadi said on Sunday he had asked the defence ministry to request coalition involvement, but "no air support was provided".

Asked if it would be better if air strikes by coalition aircraft did take place, Saadi said: "Of course... the Americans have advanced equipment, they have AWACS (surveillance) aircraft."

"They are able to locate the targets exactly" and accurately strike them," Saadi told the AFP news agency.

Saadi complained that support from the Iraqi air force had been "limited" and not always sufficiently accurate.

He said he thought the reason there had been no coalition strikes to support the two-week-old Tikrit operation was political and not military.

Shia Iran has been Baghdad's main foreign partner in the operation and Tehran's top commander in charge of external operations, Qassem Soleimani, has been omnipresent on the front lines.

Officials in Washington have expressed unease at the level of Iranian involvement in Tikrit, an overwhelmingly Sunni city which was executed dictator Saddam Hussein's hometown.

Coalition support elsewhere

Coalition air strikes have supported several other operations to reclaim ISIL-held territory in Iraq in recent months, including some in which Iran-backed Shia militias were involved.

Karim al-Nuri, a top leader from the Badr militia and the spokesman of the volunteer Popular Mobilisation units, said on Saturday it would take no more than "72 hours" to flush out holdout ISIL fighters in Tikrit.

The Popular Mobilisation units account for the bulk of the manpower involved in the two-week-old offensive to wrest back Tikrit, alongside army, police, militia and tribal forces.

Nuri's comments came as the Reuters news agency reported that Iraqi forces and mainly Shia militia battling ISIL had paused their offensive for a second day on Saturday as they awaited reinforcements.

A source in the local military command centre told Reuters military commanders had "reached a decision to halt the operation until a suitable, carefully set plan is in place" to break into central Tikrit.

Army and militia forces pushed into Saddam Hussein's home city on Wednesday in their biggest drive yet against the fighters who seized large swaths of land in Iraq and neighbouring Syria last year in a lightning campaign halted just outside Baghdad.

More than 20,000 troops and allied militias entered the city about 160km north of the capital after retaking towns to the south and north in a campaign launched nearly two weeks ago.

Source: Agencies