BAGHDAD -- The United Nations 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 in the past month has driven Iraq into its deepest crisis since the last American troops left in 2011. The violence has left Sunni-Shiite tensions soaring and raised 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 with 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.

The U.N. special envoy to Iraq, Nickolay Mladenov, called on lawmakers to attend the meeting and 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. Al-Maliki's opponents, and even many of his former allies, accuse him of trying to monopolize power and alienating the Sunni community, and they are calling for him not to seek a third consecutive term.

Al-Maliki has so far refused to withdraw his candidacy, claiming he has a mandate after his State of Law bloc captured the most seats in April elections.

Lawmakers appear unlikely to achieve a major breakthrough today, setting the stage for further political wrangling in the days and weeks ahead.

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. The front lines have largely stabilized since their offensive encountered greater resistance in majority Shiite areas, though heavy fighting rages on.

In Baghdad, gunmen in four-wheel-drive vehicles raided two buildings in a housing complex in the Zayounah neighborhood, killing at least 33 people, including 29 women, police said. They said at least 18 people were wounded.

An Interior Ministry official and hospital officials confirmed the casualty figures.

The motive behind the killings was not immediately clear, but police said there are suspicions that the buildings were being used as a brothel.

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

Also 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 -- 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 about 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.

Ramadi is the capital of Anbar, an overwhelmingly Sunni province and one of the most active battlefields in Iraq. The Islamic State of Iraq and the Levant and other Sunni militants seized control of the Anbar city of Fallujah and parts of Ramadi in January. The government has since reasserted its control of Ramadi, but Fallujah remains in insurgent hands.

The vast majority of volunteer fighters are Shiites who have answered a call from the country's top Shiite cleric, Ayatollah Ali al-Sistani, to defend Iraq from the Sunni militants led by the Islamic State, which has unilaterally declared the establishment of an Islamic state ruled by Shariah law in the territory it controls on the Iraq-Syria border.

The government's reliance on Shiite militias -- who have deployed in sizable numbers to several cities across the country -- to help counter the militant threat has ramped up sectarian tensions, fueling fears that Iraq could return to the sectarian bloodletting that engulfed the country in 2006-07.

A Section on 07/13/2014