Q&A: Karachi violence
Pakistan's commercial capital Karachi has seen a recent surge in violence, much of it involving armed gangs linked to rival ethnic and political groups. At least 300 people were killed in the city in July - 200 of them thought to be victims of targeted killings and clashes, according to local media.
The paramilitary Rangers and Frontier Constabulary have been given police powers to try to stop the violence, which has been going on for months and shows no sign of abating.
Why is Karachi important?
Karachi is Pakistan's largest city by far, with a population of over 18 million and rising, and is its main economic hub. It is also the capital of the southern province of Sindh - the port of Karachi on the Arabian Sea is used as an entry point for crucial supplies for the US war effort in Afghanistan.
Pakistan's Prime Minister Yousuf Raza Gilani has made ending the violence a priority, saying the country "cannot afford a breakdown of law and order" in the city.
But BBC correspondents say the government appears unwilling or unable to stop the violence, which has wreaked havoc. Security officials say this is because senior politicians are protecting many of those involved in the killings.
How many lives have been lost?
The independent Human Rights Commission of Pakistan (HRCP) said 490 people had been killed in targeted killings in Karachi during the first half of 2011, compared with 748 in 2010.
BBC correspondents say the violence is becoming increasingly indiscriminate. As well as political activists being targeted - shopkeepers, cafe owners, truck drivers and even pedestrians have all been gunned down.
What's behind the violence?
The violence is essentially a turf war between rival political groups and heavily armed gangs linked to them.
There is a clear ethnic element as the Muttahida Qaumi Movement (MQM), the main power in Karachi, is the party of Urdu-speaking Mohajirs - the majority of the city's population.
While the city's Pashto-speaking Pashtuns favour the Awami National Party (ANP).
The Pakistan People's Party (PPP) - the ruling party at federal and provincial level - is accused of supporting the Pashtuns in an attempt to erode the MQM's street power in Karachi. The PPP denies the allegations, saying it favours a policy of political reconciliation. The MQM was part of the PPP-led coalition in Sindh, but after nearly nine years in power it decided last month to sit on the opposition benches.
Who else may be involved?
The local political parties are believed to have a complex, mutually dependent relationship with assorted criminal syndicates variously engaged in extortion, illegal arms trading, drug trafficking and land grabbing.
But the solution to the crisis lies in the hands of politicians, according to the independent Human Rights Commission of Pakistan (HRCP).
"While gangs of land-grabbers and mafias have tried to exploit the breakdown of law and order, they do not appear to be the main directors of the horrible game of death and destruction; that distinction belongs to more powerful political groups and it is they who hold the key to peace."
Are the Taliban involved?
There is no firm proof of any Taliban involvement in the targeted killings, but they are often blamed by the government and certain parties, particularly the MQM.
The ANP has said that pointing the finger at the mostly Pashtun Taliban is part of an attempt to target Pashtun migrants who have poured into Karachi in recent years fleeing violence further north in the country.
But Karachi has also had its share of militant attacks in recent years, for which insurgents linked to the Taliban and al-Qaeda are blamed.
What measures has the government taken?
The central government has handed over the worse-hit areas of the city to the paramilitary Rangers, giving them a "free hand" to arrest the culprits.
Aerial surveillance has been put in place, rewards offered and a number of arrests have been made, according to local media.
Will the army be called in?
Some political leaders have called for the army to take control of Karachi's law and order situation. But on 7 July, Interior Minister Rehman Malik ruled out such a move, saying "targeted action" would be taken instead.
The idea of the army being called onto the streets of Karachi is unpopular - in the past the military has been accused of custodial deaths and human rights abuses.
What's the cost in economic terms?
Karachi - which has Pakistan's only operational commercial port - has frequently been brought to a standstill by the violence, resulting in heavy losses to business and industry.
Local traders and business associations say strikes and violence in 2010 led to the loss of hundreds of millions of dollars, placing further pressure on Pakistan's already beleaguered economy.
Karachi provides about half (other estimates say nearly three-quarters) of the total annual tax revenue collected by the government.
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