Pakistani police and paramilitary troops were issued "shoot on sight" orders on Friday in its largest city of Karachi after 70 people were killed in three days of ethnic and political violence.
The latest surge in violence in the southern city, plagued for years by ethnic and political strife, came after the Muttahida Qaumi Movement (MQM), Karachi's dominant party, announced last month it would quit the ruling coalition.
While violence in Karachi is endemic -- it's not unusual for six or seven people to be killed daily in political and criminal shootings -- security analyst Imtiaz Gul says the latest fighting is a battle for influence between the MQM, the Pashtun-based Awami National Party and the ruling Pakistan People's party.
The long-standing conflict among the Urdu-speaking MQM mohajirs -- descendants of immigrants from India -- ethnic Pashtuns and indigenous Sindhis has intensified in recent years, stoking concerns that a nation created on the basis of religion could splinter along ethnic lines.
Here are some facts about Karachi, the provincial capital of southern Sindh province:
WHAT IS AT STAKE?
Karachi, according to some officials, contributes 68 percent of the government's total revenue and 25 percent of gross domestic product. It is home to the central bank, the main stock exchange and is also the main industrial base.
The country's two main ports are in Karachi and it is the major transit point for supplies for U.S. forces in Afghanistan. The U.S. Defense Department says the U.S. military sends 60 percent of supplies for the Afghan war through or over Pakistan, including 40 percent of its fuel. Most of it is shipped through Karachi.
That means there's a lot of money -- and power -- in play.
"This can be summed up in five words - a turf war between political parties," Gul, author of "The Most Dangerous Place: Pakistan's Lawless Frontier" told Reuters.
"This is a turf war between the MQM, and ANP and the PPP, for territory - for political space in this big city."
The PPP is trying to redraw electoral districts, which would disadvantage the MQM, he said, and many local political leaders have connections to the criminal gangs that run rampant in the city.
The ANP -- allied to the PPP -- is also traditionally opposed to the dominant MQM, which adds to the strife.
The mohajirs constitute the largest single group in Karachi and are represented by the MQM which last month quit the ruling coalition led by Pakistan People's Party of President Asif Ali Zardari at the center as well as the Sindh government.
The mohajirs are descendants of refugees from northern India who migrated to Karachi, Hyderabad and Sukkur in Sindh province, when Pakistan was formed in 1947.
Pakistan was the creation of the Muslim elite from British-ruled India. In the initial years after the formation of Pakistan, when Karachi was the capital, the mohajir elite dominated political power in Pakistan.
After the Pakistani army under General Ayub Khan seized power in the late 1950s, the mohajirs found themselves increasingly marginalized by a combination of Punjabis and Pashtuns. After the capital was shifted from Karachi to Islamabad, the mohajirs lost most of their political power and were much of their influence in the federal bureaucracy.
Since then, they have fought to consolidate their power base in Karachi, both through the ballot as well as in street battles, principally with the Awami National Party, the main Pashtun group. But it also sometimes clashed with supporters of the ruling Pakistan People's Party as well as Sindhi nationalist groups.
INFLUX OF PASHTUNS/TALIBANISATION
Karachi's melting pot became more volatile following an influx of Afghan and Pakistanis Pashtuns from the northwest Khyber-Pakhtunkhwa province and the Federally Administered Tribal Areas along the border following the 1979 invasion of Afghanistan by the Soviet Union.
Army operations against the Pakistan Taliban in 2008 and a stepped-up U.S. drone campaign created another Pashtun influx.
According to some estimates, 3.5 million Pashtuns live in Karachi, making it the single largest concentration of Pashtuns anywhere.
Many Pashtuns have sympathies with the Deobandi Taliban, the MQM says, warning that the metropolis is slowly being Talibanized.
The main Pashtun party, the Awami National Party, however, is staunchly secular and at war with the Taliban in the country's northwest. They complain that the MQM has kept them out of city government positions and failed to deliver services to Pashtun areas of the city.
Karachi's Citizens-Police Liaison, a watchdog group, says more than 1,100 people were killed in ethnic violence in the city in 2010, the worst toll in 15 years, with political and religious leaders among the victims.
Islamist militant violence in Karachi also increased in 2010 ending a period of quiet in the preceding two years when guerrilla groups focused more on cities in the northwest. In November, a suspected Taliban suicide car bombing demolished a crime investigation department compound where senior militants are interrogated. At least 18 people were killed and 100 wounded.
Following the death of al Qaeda leader Osama bin Laden by U.S. Navy SEALs in a secret mission in the northwestern garrison town of Abbottabad on May 2, a small group of militants attacked a major navy base in the Karachi. The militants held out for 16 hours at the base against 100 commandos and rangers.
The city, home to more than 18 million people, was a main target of al Qaeda-linked militants after the September 11, 2001, attacks on the United States, when Pakistan joined the U.S.-led campaign against militancy, and foreigners were attacked in the city several times.
(Compiled by Sanjeev Miglani; additional Reporting by Rebecca Conway; Editing by Chris Allbritton)