Baghdad, Iraq ? Mortar battles have erupted between Shiite and Sunni neighborhoods in Baghdad, and the once-mixed city is reeling as the two sides adopt the weapons and tactics of urban civil war.

Throughout the capital and in towns and villages within a 50-mile radius of Baghdad, whole populations have shifted as Shiites and Sunnis flee violence from death squads and suicide bombers to the safety of places where their Islamic sect is the majority.

The highly portable, though inaccurate, mortar is increasingly the weapon of choice as Shiite and Sunni populations separate, because it allows sectarian fighters to fire into a district from a distance.

Mortars can be quickly pulled from the trunk of a car and fired over several miles, causing death and destruction without the dangers of close-quarters combat or the sacrifice of a suicide bomber.

Across the Tigris River, in the Kazimiyah neighborhood – site of the most important Shiite shrine in Baghdad – retaliatory mortar rounds have rained down daily as well.

Other Shiite strongholds in eastern Baghdad, the Shaab neighborhood and Sadr City, are regularly bombarded as is the dangerous Sunni stronghold of Dora, in south Baghdad.

Iraqi volunteers bury 176 bodies Friday in the Shiite holy city of Najaf, 100 miles south of Baghdad. The victims of recent sectarian violence were brought from Baghdad to Najaf for the funeral.

The attacks that have driven the two Muslim sects away from each other in the capital skyrocketed after the Feb. 22 bombing of a revered Shiite shrine in Samarra, north of Baghdad.

The destruction of the golden-domed mosque enraged Shiites, particularly members of the Mahdi Army militia. The militia, loyalists of anti-American Shiite cleric Muqtada al-Sadr, stormed out of their Sadr City stronghold and have been on a rampage of revenge killing ever since. Sunnis have fought back with equal vengeance.

The Mahdi Army and the larger, Iranian-trained Badr Brigade of Iraq’s largest Shiite political bloc, the Supreme Council for the Islamic Revolution in Iraq, also have sunk deep roots in the country’s police and security forces.

The militia members and offshoot death squads have been largely responsible for running Sunnis from neighborhoods where they were a minority. Sunni insurgents, meanwhile, have been attacking Shiites throughout Iraq, including in Sunni-dominated neighborhoods, in what looks increasingly like a successful bid to ignite a civil war.

Iraq’s Immigration Ministry says about 1.5 million people are internal refugees, while the United Nations says a similar number of Iraqis have fled the country altogether. That would be about 12 percent of Iraq’s prewar population of 26 million, and both figures are probably low estimates.