Iraq's new President Fouad Massoum on Monday snubbed the powerful incumbent Prime Minister Nouri al-Maliki and nominated the deputy parliament speaker as the new prime minister, raising fears of more government infighting as Maliki refuses to leave office and the country faces the threat of Islamic State fighters, Sunni insurgents who have taken over large parts of northern Iraq.

In a televised address, Massoum nominated Haider al-Abadi, who was selected by a coalition of Shia political parties, and gave him 30 days to form a new government.

The ceremony came hours after the embattled Maliki delivered a surprise speech at midnight accusing Massoum of blocking his reappointment as prime minister and carrying out "a coup against the constitution and the political process."

Maliki followed his speech by deploying militias and his elite security forces in the streets of Baghdad on Monday and partially closing two main roads— popular spots for pro- and anti-government rallies — as hundreds of his supporters took to the streets, raising fears that he might use force to stay in power.

"We are with you, Maliki," they shouted, waving posters of him and singing and dancing.

Despite angrily insisting that he should be nominated for a third term, Maliki, a Shia, has lost support in parliament, with the main coalition of Shia parties turning against him and with U.S. President Barack Obama's administration pressuring him to step aside.

Abadi, an ethnic Kurd, pledged to form a government to "protect the Iraqi people." He was nominated for the post by the Iraqi National Alliance, a coalition of Shia parties that includes Maliki's State of Law party.

Political tension in Baghdad escalated Monday as Mohammed al-Ogeili, a lawmaker from the coalition, rejected Abadi's nomination, arguing that the move "runs against the constitution" because the State of Law party is the largest bloc and the National Alliance has no right to present any candidate.

"This decision would lead the country to a big problem, and the president bears full responsibility for this situation," he told The Associated Press.

Hakim al-Zamili, a lawmaker with the Shia Sadrist movement, however, countered that with 180 seats, the alliance could nominate its own candidates and the institutions of the state should respect their choice.

"The security forces and government bodies belong to the Iraqi people, and they should not interfere in politics," he said when asked whether Maliki might use force to stay in power.

Washington is losing patience with Maliki, who has inflamed Iraq’s current crisis by monopolizing power and pursuing a sectarian agenda that has alienated the country's Sunni and Kurdish minorities, according to critics.

Speaking to reporters in Sydney, U.S. Secretary of State John Kerry said the U.S. stands "absolutely squarely behind President Massoum."

"What we urge the people of Iraq to do is to be calm," Kerry said. "There should be no use of force, no introduction of troops or militias into this moment of democracy for Iraq."

Kerry said that a new government "is critical in terms of sustaining the stability and calm in Iraq" and that "our hope is that Mr. Maliki will not stir those waters."

The United Nations special representative for Iraq, Nickolay Mladenov, said Iraq's "special forces should refrain from actions that may be seen as interference in matters related to the democratic transfer of political authority."

Also Monday, senior U.S. officials said the Obama administration, which launched airdrops and airstrikes last week to support Kurdish and Iraqi forces battling fighters from the Islamic State, has begun directly providing weapons to the Kurdish peshmerga forces, which have started to make gains against Islamic State, an Al-Qaeda breakaway group that controls much of the north.

U.S. airstrikes have reinvigorated Iraqi Kurdish forces battling the Islamic State, and on Sunday, Kurdish peshmerga fighters retook two towns — Makhmour and al-Gweir, some 28 miles from the Kurdish capital of Irbil — from the Sunni fighters in one of the first peshmerga victories after weeks of retreat.

The move to directly arm the Kurds underscores the level of U.S. concern about Islamic State gains. The officials wouldn't say which U.S. agency is providing the arms or what weapons are being sent, but one official said it is not the Pentagon. The CIA has historically done similar quiet arming operations.

Obama cautioned Americans on Saturday that the new campaign to support security in Iraq requires military and political changes and "is going to be a long-term project."

He said Iraqi security forces need to revamp to effectively mount an offensive and that to do so, they need a government in Baghdad in which the military and people have confidence — an indication suggesting he has written off Maliki's legitimacy.

The militant advances and the political turmoil have deepened Iraq's humanitarian crisis, with some 200,000 Iraqis recently joining the 1.5 million people already displaced by violence this year.

With news wires