US Secretary of Defence Ashton Carter visited Baghdad Monday for talks on stepping up the fight against the Islamic State group in Iraq, where Washington has deployed troops to fight the jihadists.

His visit comes after a week of political turmoil that has been a setback for Prime Minister Haider al-Abadi, and the US defence chief has previously stressed the need to support the embattled premier.

The United States heads an international coalition that is carrying out strikes against IS and also providing training and other assistance to forces fighting the jihadists in both Iraq and neighbouring Syria.

Carter met with Abadi and was also to hold talks with Defence Minister Khaled al-Obeidi on increasing American military assistance to Iraq ahead of the key battle for second city Mosul, which IS holds.

"The fight for Mosul is critical... and it's a very large urban scenario," a senior defence official said.

"We are going to need to be more aggressive."

Carter arrived in Baghdad from the United Arab Emirates, his first stop on a Gulf tour during which he will seek to shore up support for Iraq.

He has said that "the success of the campaign against (IS) in Iraq does depend upon political and economic progress as well", and that "it's important that we continue to support" Abadi.

The premier has sought to replace the current cabinet of party-affiliated ministers with a government of technocrats, but has faced major opposition from powerful parties that rely on control of ministries for patronage and funds.

Abadi's cabinet efforts were overshadowed by days of chaos in parliament, where lawmakers held a sit-in, brawled in the chamber and sought to sack the speaker.

The premier called on Monday for parliament to put aside its differences and do its job, saying he hoped a new cabinet would be approved "in the coming days".

In addition to major security and political challenges, Iraq also faces a serious economic crisis caused by low oil prices and years of mismanagement and corruption by officials.

- Boots on the ground -

IS overran large areas north and west of Baghdad in 2014, but Iraqi forces have since regained significant ground from the jihadists.

Iraqi forces have begun preparatory operations in Nineveh province, of which Mosul is the capital, but the actual assault to retake the city is not expected for months, and possibly not until next year.

The United States has deployed some 3,900 troops to Iraq, most of them in advisory and support roles.

But Washington has also sent in special forces to carry out raids against IS, and US Marines have deployed to provide artillery support for Iraqi troops.

US President Barack Obama repeatedly pledged that there would be no "boots on the ground" to combat IS, but US forces are engaged in combat with the jihadists and two American military personnel have already been killed.

An American Marine was killed in a rocket attack in northern Iraq last month, and a US special forces soldier wounded during a raid last year later died.

Both the raid and the attack on the Marine artillery position only came to light after American personnel were killed.

US-led forces invaded Iraq in 2003, overthrowing dictator Saddam Hussein and unleashing an insurgency and years of brutal sectarian violence due to poor planning and a lack of understanding of the country.

Rampant violence was eventually brought under control, and American forces withdrew at the end of 2011 after talks on a residual troop presence broke down over Washington's insistence that they have parliament-approved immunity.

Carter's trip to Iraq is the latest in a series of visits by senior Western officials in recent days.

US Secretary of State John Kerry travelled to Iraq two weeks ago to show support for the crisis-hit government, vowing to turn up the heat on IS.

And French Defence Minister Jean-Yves Le Drian came to Iraq last week, saying that Mosul and Raqa, IS's main stronghold in Syria, "must fall" this year.