— Iraq airlifted 4,000 volunteers to an embattled city west of Baghdad to help bolster government forces locked in a running battle with Sunni militants there, authorities said Saturday.

About 2,500 of the volunteers arrived in Ramadi, 70 miles west of the capital, on Friday and were joined by 1,500 Saturday, said Gen. Rasheed Flayeh, the commander of operations in Anbar province.

The vast majority of volunteers are Shiites who have answered a call from the country’s top Shiite cleric, Grand Ayatollah Ali Sistani, to defend Iraq from the Sunni militants who have overrun much of the country’s north and west over the past month. The blitz is led by the Islamic State extremist group, which has unilaterally declared the establishment of an Islamic state ruled by sharia in the territory it controls straddling the Iraq-Syria border.

The government’s reliance on Shiite militias to help counter the threat from Sunni militants has raised sectarian tensions and stoked fears that Iraq could return to the wholesale sectarian bloodletting that engulfed the country in 2006 and 2007.

Ramadi is the capital of Anbar, an overwhelmingly Sunni province. The Islamic State and other Sunni militant groups seized control of the Anbar city of Fallujah and parts of Ramadi in January. The government has since reasserted control of Ramadi, but Fallujah remains in insurgent hands.

The militant onslaught over the past month has touched off Iraq’s worst crisis since the last U.S. troops left in 2011 and sapped public — and international — confidence in Shiite Prime Minister Nouri al-Maliki.

Iraq’s new parliament is scheduled Sunday to hold its second session since the elections 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.

On Saturday, the United Nations’ special envoy to Iraq, Nickolay Mladenov, warned that failure to quickly elect new leadership “risks plunging the country into chaos.”

How the Islamic State is carving out a new country

— Associated Press