Washington  - Thursday's elections in Afghanistan are seen as a critical test of whether the country is politically stabile enough to make progress in fighting off the Taliban and rebuilding a war- ravaged society.

The US military has beefed up its presence throughout Afghanistan to make voters safer, hoping that whatever the results in presidential and provincial elections, the outcome will be viewed as legitimate.

"It looks like more Afghans will be able to vote than had been the case before the recent deployment of additional US forces, and obviously that's an encouraging development," US Defence Secretary Robert Gates said.

The conflict in Afghanistan is among President Barack Obama's top foreign policy priorities as he winds down the war in Iraq and steps up US efforts in Afghanistan. Since taking office, Obama has revised US policies in the country to more closely tie military progress with development of civil institutions and the economy, while targeting drug cultivation and corruption.

At the same time, he ordered 17,000 more US troops to Afghanistan and replaced the top commander, installing General Stanley McChrystal, who has more expertise in counterinsurgency operations than his predecessor.

Gates has said that the next year will be decisive in determining Afghanistan's future, whether it can be turned into a secure environment or fall under greater control of the Taliban.

A resurgent Taliban coupled with a more aggressive US policy to root out the militants has seen stepped up fighting. July was the deadliest month for US forces since the war began in October 2001.

Afghan President Hamid Karzai, who is seeking a second five-year term but does not enjoy the strong support he enjoyed from the Bush administration, is trying to fend off a strong challenge from former foreign minister Abdullah Abdullah, and a second rival, former finance minister Ashraf Ghani. The trio are the leading candidates among about three dozen.

A US poll last week showed Karzai with 45 per cent to 25 per cent for Abdullah, but short of the 50 per cent needed to avoid a runoff. Karzai has reportedly fallen into disfavour with the Obama administration, in part because of what is believed to be widespread corruption in his government.

But US officials have gone to great lengths to state that Washington does not have a preferred candidate, saying the most important result is that the process is fair and embraced by the Afghan people.

"The United States of America remains impartial in this election. We do not support or oppose any particular candidate," Secretary of State Hillary Rodham Clinton said Monday. "Like the Afghan people, we want to see credible, secure and inclusive elections that all will judge legitimate."

Karzai has stoked concerns by allying himself with former warlords with questionable human-rights records, most notably Afghan Uzbeki General Abdul Rashid Dostum, who returned Sunday to Afghanistan from exile in Turkey.

Karzai has evidently enlisted Dostum's support to win over ethnic Uzbekis. But Dostum has been accused of killing thousands of Taliban prisoners as the militant regime was being ousted by US-led forces in 2001.

The US embassy in Kabul condemned Dostum's return: "The United States has made clear to the government of Afghanistan its serious concerns about the prospective role of Mr Dostum in today's Afghanistan, and particularly during these historic elections."

Speaking to a group of US war veterans Monday in Phoenix, Arizona, Obama said the United States is in for a long and difficult fight in Afghanistan and must remain committed to the country regardless of the election's outcome.

"There will be more difficult days ahead," Obama said. "The insurgency in Afghanistan didn't just happen overnight. And we won't defeat it overnight. This will not be quick, nor easy." (dpa)