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By Peter Graff
KABUL, April 27 (Reuters) - The United Nations said on Tuesday it had temporarily shut its office in the southern Afghan city of Kandahar and withdrawn some foreign staff for their safety, as security deteriorates ahead of a major NATO offensive.
Following are answers to questions about the planned military campaign, which will unfold during the coming months:
HOW IMPORTANT IS IT?
The Kandahar operation is the central objective of U.S. and NATO commander General Stanley McChrystal's campaign plan to turn the tide in the war this year using 30,000 reinforcements pledged by President Barack Obama in December.
It will be by far the biggest offensive of the war so far, directly involving more than 23,000 ground troops, including about 8,500 Americans, 3,000 Canadians and 12,000 Afghan soldiers and police.
The Chairman of the U.S. Joint Chiefs of Staff, Admiral Mike Mullen, describes the offensive as "the cornerstone of our surge effort and the key to shifting the momentum", which Washington hopes will eventually push the Taliban to agree to peace talks. Kandahar was the spiritual home of the Taliban movement when they ruled Afghanistan from 1996-2001, and has huge symbolic importance in the country. It forms the heartland of the Pashtuns -- Afghanistan's largest ethnic group and traditional rulers -- and is also the home town of President Hamid Karzai.
In an assessment of the war last year, McChrystal described Kandahar as the Taliban's main geographical objective.
Militants control much of the city of 500,000 people, as well as many rural regions around it, making it the part of the country where the greatest concentration of people now live outside government control.
McChrystal's counter-insurgency strategy depends on securing population centres to allow the government to extend its reach, open areas to access for trade and development projects, and win over the support of the people.
WHAT IS THE MILITARY SITUATION IN KANDAHAR LIKE NOW?
A mainly Canadian force of about 3,000 troops has operated in Kandahar province for four years, taking high casualties but lacking the manpower to secure such a large city and its outskirts. Taliban influence has grown rapidly during that time, and militants are now stronger in the province than at any time since they were driven from power in 2001.
Over the past year more than 5,000 extra U.S. ground troops have arrived in the province and have begun securing rural districts that control routes leading into the city, although swathes of those agricultural areas are still in militant hands.
Inside the city itself there is very little presence of Western forces. Many of the city's teeming residential districts are almost entirely out of bounds for Afghan police, especially at night.
WHEN WILL THE OPERATION BEGIN?
NATO commanders say initial "shaping operations" are already under way, including efforts to reach out to residents, military operations to clear areas in the rural outskirts, and special forces raids to capture and kill Taliban leaders.
The main "clearing phase" in urban areas will begin around the start of June, with the arrival of an additional U.S. Army Brigade Combat Team of about 3,500 troops that will spearhead the military campaign in urban areas alongside Afghan police.
HOW WILL IT UNFOLD?
U.S. and NATO commanders have tried to play down the military aspects of the upcoming operation, insisting the emphasis is on political reforms. Nevertheless, the operation will still be the biggest ground offensive in nearly nine years of war.
The 8,000 NATO troops already in Kandahar province will mostly remain in rural areas, guarding routes into the city, while the additional 3,500-strong U.S. army brigade pushes into urban districts in the company of 6,700 Afghan police.
Unlike the last big offensive, which began with a massive airborne assault in neighbouring Helmand province in February, NATO commanders stress that the Kandahar operation will not have an abrupt start but will unfold gradually.
They hope negotiations on the ground will allow troops to advance into urban sectors of Kandahar with minimal fighting, although they say they also expect a certain amount of combat in the city if militants choose to resist.
In the rural districts, commanders predict an increased level of combat as fighters either flee the city or attempt to reinforce it. NATO units in the rural areas will also launch operations to clear villages now under insurgent control.
NATO commanders would like to see the clearing operations finished by the start of the Muslim holy month of Ramadan in August, and be followed by steps to improve governance and provide services to the population.
The Taliban have vowed to fight against the advancing NATO troops, and have already begun a campaign of bomb attacks, commando raids and assassinations in recent weeks.
WHAT ABOUT LOCAL GOVERNMENT?
NATO officials constantly reinforce the message that the military phase of the operation is only the first step, and the true aim is to bring credible government to areas now under Taliban control.
They say the Taliban have won support from Pashtun tribes in Kandahar who feel they have been shut out of provincial power by rival clans, including Karzai's own family.
The main goal of the political reform plan is to make the provincial government more inclusive, so that tribes and groups who sought protection from the Taliban in the past feel more secure and cast their lot with the government.
The most powerful person in Kandahar is now the head of the provincial council, President Hamid Karzai's half-brother, Ahmad Wali Karzai, a businessman who has long denied persistent reports of links to southern Afghanistan's drugs trade.
U.S. officials say they would like to see his influence reduced as provincial government is reformed, but they do not expect him to be removed. (Additional reporting by Adam Entous; Writing by Peter Graff) (For more Reuters coverage of Afghanistan and Pakistan, see: here)