Iraq crisis: Embattled PM Nouri Maliki attacks president
Iraqi PM Nouri Maliki has said he will take the country's president to court for violating constitutional rules.
In an address on state TV, Mr Maliki criticised Fuad Masum for not intervening after parliament failed to give him a third term as PM.
Mr Maliki is facing calls to step down amid the jihadist insurgency in the north.
The US, which has urged Iraq to form an inclusive government, issued a statement backing Mr Masum.
Pro-Maliki security forces took up positions around Baghdad shortly before Mr Maliki's speech.
Earlier, Iraqi Kurds appealed for international military aid to help defeat the Islamist militants.
The US has already launched four rounds of air strikes targeting Islamic State (IS) fighters near Irbil, the capital of Iraqi Kurdistan.
A Kurdish official said recent US air strikes on IS militants in Nineveh province had helped the Kurdish Peshmerga fighters retake the towns of Gwer and Makhmur after heavy fighting.
Mr Maliki said he intended to submit an official complaint on Monday against President Masum.
He accused him of "committing a clear constitutional violation for the sake of political calculations and... giving priority to the interests of some groups at the expense of the higher interests of the Iraqi people".
Mr Maliki's coalition won the most seats in April's elections but parliament has not agreed to give him a third term.
Mr Masum had violated the constitution twice, by extending a 7 August deadline for asking the biggest political bloc to nominate a prime minister and then by failing to ask the head of that bloc to form a government, Mr Maliki said.
"This attitude represents a coup on the constitution and the political process in a country that is governed by a democratic and federal system," Mr Maliki said.
"The deliberate violation of the constitution by the president will have grave consequences on the unity, the sovereignty, and the independence of Iraq and the entry of the political process into a dark tunnel."
Shia militiamen and security forces loyal to Mr Maliki reportedly appeared at key centres in Baghdad. There were no reports of violence.
Critics say Mr Maliki, a Shia, has precipitated the current crisis through sectarian policies and there have been calls by Sunnis, Kurds, and even fellow Shia for him to stand down.
The West has also piled pressure on Iraq's leaders to form a power-sharing government in the face of Sunni militants who now control a vast swathe of the country.
In Washington, deputy state department spokesman Marie Harf said it was "closely monitoring" the situation in Iraq.
"The United States fully supports President Fuad Masum in his role as guarantor of the Iraqi constitution," she said.
"We reaffirm our support for a process to select a prime minister who can represent the aspirations of the Iraqi people by building a national consensus and governing in an inclusive manner."
Earlier on Sunday, Kurdish forces said they had regained Gwer and Makhmur.
It is the first time Kurdish forces have regained ground from IS since US military action was authorised on Thursday.
In western Iraq, minority religious groups, such as the Yazidis, have been forced from their homes, prompting international aid drops.
Witnesses told the BBC that thousands of refugees near Sinjar had escaped to safer areas.
The US air strikes have been the first direct American involvement in a military operation in Iraq since their withdrawal from the country in late 2011.
US President Barack Obama authorised the strikes last week after members of the Yazidi sect were forced to flee Sinjar into the surrounding mountains.
- The majority are Chaldeans, part of the Catholic Church
- Numbers have fallen from around 1.5 million since the US-led invasion in 2003 to 350,000-450,000
- In Nineveh province, they live mainly in towns such as Qaraqosh (also known as Baghdida), Bartella, al-Hamdaniya and Tel Kef
- Secretive group whose origins and ethnicity are subject to continuing debate
- Religion incorporates elements of many faiths
- Belief that God's will is carried out by seven angels
- Most important among them is the Peacock Angel, considered by some Muslims and Christians to be the devil but who Yazidis say was redeemed
- Because of this, Yazidis are viewed by some as devil worshippers
- There are estimated to be around 500,000 Yazidis worldwide, most living in Iraq's Nineveh plains