Haider al-Abadi.

BAGHDAD — Nuri al-Maliki finally bowed to pressure within Iraq and beyond on Thursday and stepped down as prime minister, paving the way for a new coalition that world and regional powers hope can quash a Islamist insurgency that threatens Baghdad.

Maliki ended eight years of often divisive rule and endorsed fellow Shi’a Haider al-Abadi in a televised speech, during which he stood next to his successor. Earlier, a leading figure in the Sunni minority said he had been promised U.S. help to fight the Islamic State militants.

Though there was no immediate comment from Washington, the remarks by the governor of the Sunni heartland province of Anbar, Ahmed Khalaf al-Dulaimi indicated that such a move could revive cooperation between Sunni tribes, the Shi’a-led authorities and U.S. forces that was credited with thwarting al-Qaeda in Iraq several years ago.

He said his decision was aimed at preserving the country’s unity.

“I announce before you today, to ease the movement of the political process and the formation of the new government, the withdrawal of my candidacy in favor of brother Dr. Haider al-Abadi,” said Maliki.

al-Dulaimi said his request, made in meetings with U.S. diplomats and a senior military officer, included air support against the militants who have a tight grip on large parts of his desert province and northwestern Iraq.

Dulaimi said the Americans had promised to help. There was no immediate confirmation from U.S. officials on a day when President Obama said troops planning an evacuation of refugees further north were standing down as U.S. air strikes and supply drops had broken the “siege of Mount Sinjar.”

Governor Dulaimi said in a telephone interview with Reuters: “Our first goal is the air support. Their technology capability will offer a lot of intelligence information and monitoring of the desert and many things which we are in need of.

“No date was decided but it will be very soon and there will be a presence for the Americans in the western area.”

After its capture of the northern metropolis of Mosul in June, a swift push by the Islamic State to the borders of the autonomous ethnic Kurdish region alarmed Baghdad and last week drew the first U.S. air strikes on Iraq since the withdrawal of American troops in 2011.

U.S. involvement in Anbar is a far more sensitive matter.

The region, sparsely populated and forming much of Iraq’s border with Syria, was deeply anti-American during the U.S. occupation. Tribal leaders and local people saw the replacement of Saddam Hussein by a U.S.-backed leadership dominated by Iraq’s Shi’a majority as a threat and took up arms. Al-Qaeda fighters flooded in to join them.

The United States mounted its biggest offensive of the occupation against a variety of Islamist militants in the Anbar city of Falluja, just west of Baghdad. U.S. soldiers experienced some of their fiercest combat since the Vietnam War.

Eventually, the U.S. military was able to persuade some of its most diehard Sunni opponents to turn against al-Qaeda.

The strategy brought a period of calm. 

Maliki resisted months of pressure to step down from Sunnis, Kurds, some fellow Shi’s, Iran and the United States.

The Islamic State, disowned by al-Qaeda as too radical after it took control of large parts of Syria, capitalized on its Syrian territorial gains and sectarian tensions in Iraq to gain control of Falluja and Anbar’s capital Ramadi early this year.

Iraq’s president nominated Abadi, who is seen as a moderate Shi’ite with a decent chance of improving ties with Sunnis.

Abadi is in the sensitive process of trying to form a new government in a country where sectarian tensions are rising; bombings, kidnappings and executions are part of daily life.

The new prime minister faces the challenge of trying to rein in Shi’a militias accused of kidnapping and killing Sunnis and persuading the once dominant Sunni minority that they will have a bigger share of power.

Dulaimi was especially concerned by the militants’ determination to seize control of Anbar’s Haditha dam: “The situation in Haditha, where the dam is, is controlled by security forces and tribes. But the problem is how long can they endure the pressure?” said Dulaimi.

“I held several meetings since one month ago with the American embassy and the commander of the central troops all in this regard, and very soon there will be a joint coordination centre and operations in Anbar. They gave a promise.”

Aside from strong momentum built up in the north and control of large parts of the west, the Islamic State has threatened to march on Baghdad.