KANDAHAR, Afghanistan - The fight for Kandahar, the Taliban heartland, is seen as crucial to a U.S. strategy to end the nearly nine-year costly conflict.

In December, President Barack Obama ordered 30,000 extra American troops into Afghanistan, where the vast majority are disembarking in the south, pushing the total nationwide NATO deployment to 150,000 by August.

U.S.-led NATO troops are preparing a major offensive this summer in this province. The U.S. force total in Afghanistan has roughly tripled since Obama took office in January 2009, and at 94,000 exceeds the 92,000 based in Iraq.

On Friday, NATO announced its forces had killed a top Taliban commander for Kandahar city, Mullah Zergay, after a raid to capture him last week sparked a gunfight.

U.S. commanders say they will try to defeat the militants with a minimal use of force in an attempt to avoid inspiring more support for the Taliban among their fellow Pashtuns.

The U.S.-NATO effort has been using a twin strategy to try to improve security, at once conducting military raids and security sweeps jointly with Afghan forces even as they try to meet local leaders to create the conditions for better government.

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Yet security is deteriorating in this, the largest city in the country's volatile south. To its western edge is the neighborhood of Kokaran, through which runs a Taliban infiltration route dominated by the insurgent movement. There is virtually no functioning government.

Apart from the attack that killed Shelter Island's Joseph Theinert Thursday, at least three other American soldiers - all between the ages of 20 and 24 - and two British soldiers died in attacks in Kandahar and the neighboring southern province of Helmand last week.

A bomb exploded yesterday outside the Kandahar governor's office, killing a policeman and wounding at least 14 civilians, officials said. Kandahar city police Chief Sardar Mohammad Zazai said explosives were strapped to a bicycle on the street outside the compound where the governor, away at the time, lives and works.

Last month, a Taliban assault on the main foreign base at Kandahar injured three Canadian soldiers and 10 civilian workers. According to the Canadian military, bomb-making materials were found in the officer's quarters at a police training academy a few miles from the base.