A trash-strewn dusty street here became a front line in recent ethnic battles that killed 100 people in four days.

Now, in the aftermath, residents speak of the street as though it is a chasm, dividing the population of this oceanside city of 18 million and even Pakistan itself.

On one side, people known as Mohajirs, long the dominant group in this economic hub, seethingly point to bullet-scarred and burned houses and demand a new province that would be theirs alone. On the other side, Pashtuns who migrated here in recent years after fleeing an Islamist insurgency in their native northwest also point to bullet holes, and some express worry that a sort of ethnic cleansing is to come.

“Now they are asking for their own province,” Adnan Khan, a Pashtun whose brother was fatally shot by unknown assailants this month, said of the Mohajirs. “Next maybe they will ask for their own country.”

Karachi, Pakistan’s most diverse city, is once more spewing violence that goes unchecked by police and is stoked by thuggish politicians. While the fierce Taliban insurgency seeks to overthrow the government from mountain hideouts hundreds of miles away, the city’s battles are laying bare the deep ethnic, political and sectarian cleavages that pose an additional threat to this fragile federation — as well as an impediment to its unity against Islamist militancy.

When Pakistan parted from India in 1947, it fused vast spans of ethnically and linguistically distinct populations under the common cause of Islam. But the state has struggled to define Islam’s role as a social adhesive. The powerful, Punjabi-dominated military, meanwhile, has aimed to suppress various nationalist movements, even while sometimes backing ethnic and sectarian groups as tools for influence. Politics remain cutthroat and largely localized. The result, some say, is a nation hobbled — and increasingly bloodied — by factionalism.

“Why are they fighting in Karachi? Because they have not become Pakistani yet. People have not become a nation,” said Syed Jalal Mahmood Shah, the Karachi-based leader of a small nationalist party that represents people native to surrounding Sindh province. Mohajirs, like Pashtuns, are themselves migrants to Karachi: They are Urdu-speaking Muslims who fled Hindu-majority India at partition.

Escalating clashes

Shifting demographics are the root of the fighting in Karachi, where an influx of ethnic Pashtuns from the war-torn region along the Afghan border is challenging the Mohajirs’ long-standing grip on the city. The struggle is waged through assassinations, land-grabbing and extortion, and it is carried out by gangs widely described as armed wings of ethnically based political parties. The Urdu speakers, represented by the dominant Muttahida Qaumi Movement, or MQM, accuse the Pashtuns of sheltering terrorists in Karachi; the MQM’s main rival, the Awami National Party, or ANP, says the city’s 4 million Pashtuns are ignored politically.

But the violence is escalating to new levels, and residents say ethnic tensions are sharpening.

The Human Rights Commission of Pakistan says 490 people were killed in Karachi in targeted ethnic or political killings in the first six months of the year.

This month’s violence erupted after the killing of an ANP activist. After fighting subsided, the MQM was accused of provoking ethnic tensions by spray-painting graffiti throughout the city calling for a separate Mohajir province — a charge that it denied.

On Wednesday, a provincial minister from the ruling Pakistan People’s Party accused Urdu speakers of trying to divide the province after having migrated to it “hungry and naked.” That sparked another daylong spiral of violence that left 15 people dead.

It also prompted yet another shutdown of a city that provides 65 percent of the revenue to Pakistan’s tanking economy, worrying the shaky civilian government in Islamabad. According to Pakistani media reports, President Asif Ali Zardari, whose party is also accused of backing gangsters in its Karachi strongholds, apologized to the MQM on behalf of the provincial minister and pleaded for unity to combat what he called Pakistan’s “real enemy” — terrorism.

National unity, though, has been elusive, despite school textbooks that depict the nation as a refuge for Muslims living in the shadow of a hostile enemy, India. Three of Pakistan’s four provinces are home to separatist or nationalist movements, and they share bitterness toward Punjab, the most populous and powerful province.

‘Failed’ nationhood

While striving to foster a national identity, the military establishment, which has ruled Pakistan for half its existence, has tried to quell nationalist movements, human rights activists say. In the southwestern province of Ba­luchistan, where a low-level insurgency rages, Human Rights Watch recently reported that 150 corpses have been found this year in what are known as “kill and dump” operations thought to have been carried out by intelligence and security forces. Zohra Yusuf, of the Human Rights Commission of Pakistan, said Baluchis also are killing Punjabi settlers there.

“What has failed is this forced onset of Pakistani nationhood,” Yusuf said.

Nowhere are the ethnic divisions as clear as in Karachi, which is also stressed by problems confronting Pakistan’s other fast-growing cities. Inflation is rising. Infrastructure has not kept pace with growth, and residents of an ethnically divided neighborhood that was the scene of vicious fighting last week, Qasba Colony, said they are supplied with just four hours of electricity a day. In parts of the Pashtun squatter settlements that rise on a hill above the neighborhood and on Karachi’s outskirts, municipal services are unavailable.

Noncombatants targeted

Karachi’s police force is too small and outgunned by the city’s gangs, said Sharfuddin Memon, an adviser to the provincial home minister, who oversees security. But Memon also said police are not “a totally independent force” — they, too, are aligned with political parties, partly out of fear.

Law enforcement authorities said the majority of the nearly 100 people killed in the second week of July were noncombatants who were targeted for their ethnicity or who were caught in the crossfire.

Mohajirs in Qasba Colony said bullets rained down for days from the Pashtun-dominated hills, atop which a red ANP flag flies. A few blocks away, Pashtuns say bullets flew from the other direction, fired from MQM weapons. People on both sides acknowledged the existence of ethnic gangs but said they were formed for self-defense.

Aisha Bibi, 45, said her son, a 22-year-old Urdu-speaking factory worker unconnected to political groups, was fatally shot when they braved gunfire to buy groceries. His death had eliminated the family’s only breadwinner, and replacing his income would be hard, she said.

Outside her house, a group of Mohajir woman railed against Pashtuns, a word they used interchangeably with “terrorist” and “Taliban.” The only solution is complete segregation and the expulsion of Pashtuns back to the northwest, they said.

“Sindhis have their own province. Punjabis have their own province. Pashtuns have their own province,” said Nusrat Siddiqui, 30. “Why not Mohajirs?”

A short drive away, Mohammed Amin, who said he has lived in Karachi for nearly two decades, tended his tiny grocery in the Pashtun area. Mohajirs used to buy from him, but no longer. His son and nephew were wounded during this month’s battle, he said wearily, and the neighborhood’s water lines have been cut off for 20 days.

“We are all poor people,” he said, gesturing toward the Mohajir areas. “But some miscreants kill people for their own vested interests.”