What is Washington's strategy for Afghanistan?

Afghanistan's presidential election on Thursday will be a test of a US strategy that has seen 30,000 extra troops arrive this year, the most violent since the overthrow of the Taliban in 2001.

The new commander of US and Nato forces in Afghanistan, General Stanley McChrystal, is expected to deliver a strategy assessment shortly after the election.

Following are some key questions and answers on the strategy:

What are the goals?

US President Barack Obama has made Afghanistan and neighbouring Pakistan his top foreign policy priority and says Washington wants to disrupt, dismantle and eventually destroy sanctuaries for Osama bin Laden's Al-Qaeda fighters there.

In order to do that, US officials say they need to ensure Al-Qaeda's Afghan Taliban allies do not return to power.

Using lessons learned from Iraq, McChrystal says he is changing the focus of military strategy from killing Taliban fighters and leaders, to protecting Afghan civilians.

"You don't really need to chase and kill the Taliban. What you need to do is take away the one thing they absolutely have to have, and that's access and support of the people," he said.

What resources are needed?

More than 30,000 extra US troops have already arrived in Afghanistan this year, raising the size of the international force for the first time to more than 100,000, including about 63,000 Americans.

The total is due to reach 110,000, including 68,000 Americans, by the end of the year. McChrystal has not ruled out asking for more after his upcoming assessment.

McChrystal has also said he wants to see a significant expansion of Afghanistan's own security forces, beyond its roughly 90,000 Afghan soldiers and similar number of police. The new US troops include 4,000 extra trainers.

How is this different to before?

McChrystal says he wants a shift away from conventional high intensity combat towards counter-insurgency operations aimed at winning the support of ordinary Afghans.

In June and July, thousands of US Marines and British troops pushed into Taliban controlled areas in southern Helmand province, the heartland of the insurgency, and are now setting up small bases in and around villages. The tactics are modelled on the US counter-insurgency approach in Iraq since 2007, when commanders began emphasising living among the population.

As part of the strategy, McChrystal has said he plans to move troops from sparsely populated areas into more densely populated areas.

One area where he may decide to reduce the US presence is in mountain valleys in the east, where US troops are thinly scattered in remote bases and have suffered high casualties.

What has forced the change?

Violence across Afghanistan this year has reached its worst levels since the Taliban were ousted by US-led Afghan forces in 2001, with record levels of foreign troop casualties and insurgents carrying out more brazen attacks.

In an interview with the Wall Street Journal newspaper this month, McChrystal said the Taliban were gaining momentum by moving from traditional strongholds in the south and east into quieter areas in the north and west.

"We've got to stop their momentum, stop their initiative. It's hard work," he told the newspaper.

What are some of the risks?

US officials acknowledge the American public could lose patience with sharply-rising death tolls if progress cannot be demonstrated soon.

The war is already politically sensitive in Britain, Washington's closest ally, which since last month suffered its worst ground combat casualties in a generation. More combat also increases the chances of civilian casualties, which could turn more Afghans against the presence of foreigners.