US Secretary of State John Kerry on Monday warned Iraqi Prime Minister Nuri al-Maliki not to cause trouble as he threw his weight behind newly-elected President Fuad Masum to help fight Islamic militants.

His comments came after Maliki announced Sunday on state television he would be filing a complaint against Masum and as troops and police massed in the capital Baghdad.

Masum's election on Thursday is another step towards forming a government which could see the embattled Maliki replaced as prime minister, even though his party won the largest bloc in April parliamentary elections.

"We stand absolutely squarely behind President Masum (who) has the responsibility for upholding the constitution of Iraq," Kerry said in Sydney, where he will attend annual US-Australia military talks.

"He is the elected president and at this moment Iraq clearly made a statement that they are looking for change."

Maliki, who has been under huge pressure to give up his bid for a third term in office, announced his plans to file a complaint to the federal court in a surprise address at 2100 GMT Sunday.

He alleged that Masum, a Kurdish politician, had twice violated the constitution, including by failing to task a prime minister-designate with forming a new government.

Meanwhile, security sources Monday said Iraqi police, army and counter-terrorism forces were deployed in unusually large numbers across strategic locations in Baghdad overnight.

Kerry urged calm and called for the constitutional process to be completed.

"Among the Shias it is very, very evident that they have three candidates or so for prime minister. None of them are Mr. Maliki," he said.

"So what we urge the people of Iraq to do is to be calm.

"There should be no use of force, no introduction of troops or militias into this moment of democracy for Iraq.

"Iraq needs to finish its government formation process and the United States will do everything possible in order to support the upholding of the constitution."

He added that Washington believed "the vast majority of the people of Iraq are united in an effort to be able to have this peaceful transition".

"We believe that the government formation process is critical in terms of sustaining the stability and calm in Iraq," Kerry said.

"Our hope is that Mr. Maliki will not stir those waters.

"One thing all Iraqis need to know -- that there will be little international support of any kind whatsoever for anything that deviates from the legitimate constitutional process that is in place and being worked on now."

Many Iraqis see Maliki as partly responsible for the recent conflict in northern Iraq, saying he institutionalised sectarianism.

The June onslaught on areas north and west of Baghdad led by the Islamic State has brought Iraq to the brink of break-up, with the government struggling to assert any authority beyond its Shiite power base.

Washington, Tehran, the Shiite religious leadership and much of Maliki's own party have withdrawn their support from him, but he has dug his heels in.

Maliki's eight years in power
Baghdad (AFP) Aug 11, 2014 - Here are the main dates of the eight years in power of Prime Minister Nuri al-Maliki in Iraq, whose president on Monday appointed Haidar al-Abadi as his successor:

--2006--

- April 22: Newly-re-elected President Jalal Talabani, a Kurd, announces that he asked Maliki, a Shiite, to form the next government, replacing Ibrahim Jaafari, who was contested by Sunnis and Kurds.

- May 21: A national unity cabinet is sworn in, dominated by Maliki's United Iraqi Alliance which won most seats in parliamentary election.

- October 11: Parliament approves a law allowing the country's 18 provinces to hold referendums to merge themselves into larger federal regions with a measure of self-government.

The law was opposed by some in the minority Sunni community, who feared that their group would be left only with a rump territory in the barren west and centre of the country.

--2007--

- August 14, 2007: At least 400 are killed in the most deadly attacks since the overthrow of dictator Saddam Hussein in the US-led invasion of 2003, targeting members of the ancient Kurdish-speaking Yazidi religious sect in the northern province of Nineveh. Al-Qaeda is blamed.

In spite of the deployment of some 155,000 US soldiers, since the blowing up of a revered Shiite shrine in Samarra, north of Baghdad, on February 22, 2006, Iraq goes through a bloody sectarian war that costs tens of thousands of lives up until 2008.

--2010--

- March 7: Parliamentary elections marred by sectarianism. Shiites vote for Maliki's State of Law Alliance and the United Iraqi Alliance, while Sunnis vote for the secular Iraqiya bloc of Iyad Allawi. Neither side has enough seats to form a government.

- November: Political leaders announce a deal on the ethnic and sectarian make-up of the three main posts -- president, prime minister, and speaker of parliament. Talabani is re-elected president and Maliki named prime minister.

- December 20: A government of national unity is set up, and completed in February, with Maliki holding the three vacant security porfolios on an interim basis.

--2011--

- February 3: The start of protests calling for improved public services, more jobs and less corruption and for broader political reforms.

- December 18: US troops complete their withdrawal, ending nearly nine years of occupation, leaving country mired in a political crisis.

A day later an arrest warrant is issued for Vice President Tareq al-Hashemi, who takes refuge in Kurdistan. Iraqiya bloc briefly boycotts the cabinet.

--2012--

- December 23: The start of major protests, particularly in the Sunni province of Anbar, demanding Maliki's ouster and accusing him of monopolising power and discriminating against Sunnis.

--2013--

- April 23: Start of a week of clashes in Hawijah in northern Iraq between security forces and anti-government protesters allegedly infiltrated by militants that leave more than 240 dead.

According to the NGO Iraq Body Count, 2013 was the deadliest year since 2008, with 9,475 civilians killed.

--2014--

- January 2-4: Iraq loses control of Fallujah and parts of Ramadi in Anbar province to Al-Qaeda-linked fighters, after security forces cleared an anti-government protest camp in December.

- April 30: Maliki wins the most seats in the first general election since US troops departed, but his State of Law alliance falls short of an overall majority.

- June 10: Hundreds of Sunni Arab militants, led by radical jihadists, seize Iraq's second biggest city Mosul as government forces take flight. They go on to seize broad swathes of territory in the north and the west. On August 8, US jets strike jihadist positions.

- August 11: President Fuad Masum tasks Abadi with forming a government, moments after he was selected as nominee for prime minister by the National Alliance bloc.