Iraqi President Fouad Massoum has said the US-led coalition would soon carry out air strikes against Islamic State (IS) in the Sunni city of Tikrit, after starting aerial reconnaissance flights this week.

A three-week offensive by Iraqi government forces and Iranian-backed Shi'ite paramilitaries has failed to flush out IS fighters from Tikrit, the birthplace of former dictator Saddam Hussein.

"Since yesterday, aerial support and reconnaissance flights started in Tikrit. They first begin with reconnaissance missions; then they compile the aerial reports; and afterwards the aerial (strike) operations start," Mr Massoum said.

Iraqi military commanders had asked for air strikes, while the Iranian-backed Shi'ite militias had publicly rejected the US role in the campaign to retake the jihadist bastion.

Faced with the deadlock, the Iraqi government had called a halt to most operations a week ago, citing concerns about civilian and military casualties.

But Mr Massoum made clear the Iraqi government had decided to ask for the US-led alliance's air support in the battle despite the strong aversion of Shi'ite paramilitary leaders, who boast the strongest fighting force in the war against IS.

"The Iraqi government along with residents of the area wanted an active contribution from the international coalition. The Iraqi government alone decides and no other force decides," Mr Massoum, a veteran Kurdish politician who became Iraq's president last summer, said.

Upon being informed of Mr Massoum's comment, Shi'ite paramilitary commander Hadi al-Amiri, one of the most powerful men in the country, who enjoys close ties with Iran, said he had no knowledge of the decision and had not been consulted.

"If we need air strikes, we will tell our government...up until now, we don't," he said.

For his part, Mr Massoum alluded to the United States' previous reluctance to participate in battles alongside Iranian-supported Shi'ite armed factions and their Iranian advisers.

"If there were any kind of hesitation in the position of the coalition to support the (Iraqi) army and volunteers in Tikrit, it seems now that this sensitivity has ended," Mr Massoum said.

"Of course, the participation of the coalition will have an impact."

The start of air strikes would mark the first active participation by the US military and Iranian advisors in the same battle space since US air strikes were carried out last August to help liberate the Shi'ite Turkmen town of Amerli.

Mr Massoum said the country was not beholden to Iran despite its neighbour's substantial contribution of weapons and advisers since IS seized large parts of northern and western Iraq last year, imperiling Baghdad.

"Iran has provided military and humanitarian help to Iraq from the first day... (But) they have no right to object to any Iraqi decision," Mr Massoum said.

The president stressed Iraq was seeking a balance among its Iranian, Western and Arab states participating in the fight against IS.

"The coordination of the Iranians is not at the expense of Iraq's independence and sovereignty. The same applies with our coordination with the coalition countries," Mr Massoum said.

The president said the timing of the air strikes would be determined by Iraqi and coalition military experts.

He emphasized the strikes would avoid targeting civilian populations despite what he called IS's attempts to use civilians as human shields.

The president said the security forces and other fighters were working hard to avoid any human rights violations.

Sunnis had accused Shi'ite paramilitary fighters of carrying out executions and burning houses during previous campaigns to expel IS from Sunni areas.

Mr Massoum said those violations were isolated and not widespread; but, despite Iraq's best efforts, he said he could not rule out the possibility of new incidents during the Tikrit campaign.

Mr Massoum added Iraq was looking at western Anbar province as its next military battle before attempting to retake the north's largest city Mosul, which IS seized last June as it swept across Sunni parts of Iraq.