The U.N. urged Iraq’s leaders Saturday to overcome their deep divisions and move quickly to form a new government that can unite the country and confront a surging militant threat, warning that failure to do so “risks plunging the country into chaos.”

The Sunni insurgent blitz over the past month has driven Iraq into its deepest crisis since the last American troops left in 2011, pushing bloodshed to levels unseen since the height of the Iraq war, sending Sunni-Shiite tensions soaring and raising the specter of a nation cleaved in three along ethnic and sectarian lines.

Iraq’s new parliament is scheduled today to hold its second session amid hopes that lawmakers can quickly decide on a new prime minister, president and speaker of parliament — the first steps toward forming a new government. It failed to make any progress in its first session, and postponed its second session until today.

U.N special envoy to Iraq, Nickolay Mladenov, called on lawmakers to forge an agreement on new leaders. He warned of dire consequences if the current political deadlock drags on.

“It will only serve the interests of those who seek to divide the people of Iraq and destroy their chances for peace and prosperity,” he said in a statement. “Iraq needs a team that can bring people together. Now is not the time for mutual accusations, now is the time for moving forward and compromising in the interest of the Iraqi people.”

Prime Minister Nouri al-Maliki, who has ruled the country since 2006, is under pressure to step aside. His government’s inability to prevent the attack, let alone roll back the militant advance, has sapped public — and international — confidence in his ability to hold Iraq together and lift it out of the crisis.

The militants, who have tapped into the deep disaffection among Iraq’s minority Sunnis with al-Maliki, have swept through most of the country’s predominantly Sunni areas in the north and west.

On Saturday, Iraqi troops supported by Shiite militiamen battled Sunni militants who had seized at least partial control of a military base outside the town of Muqdadiyah, about 60 miles north of Baghdad. The troops and pro-government fighters succeeded in pushing insurgents out of the nearby hamlet of Nofal, but the base remained split between the warring sides, police officials said.

Police and hospital officials said the bodies of 16 pro-government fighters — a mix of soldiers and militiamen — killed in the fighting were taken to the morgue in Muqdadiyah, and another 15 were taken to the provincial capital of Baqouba. They said a family of five, including three children, was killed in government airstrikes on Nofal.

The officials spoke on condition of anonymity because they were not authorized to brief the media.

To the west of Baghdad, the government airlifted some 4,000 volunteers to Ramadi to boost their forces trying to defend the city from militant attack, said Gen. Rasheed Flayeh, the commander of operations in Anbar province. The operation began Friday and finished Saturday.