'The fighting has been fierce,' Obama said. 'More Americans have given their lives.'

Afghans will vote in elections Thursday as incumbent President Hamid Karzai continues to hold a lead in surveys, although he is expected to be strongly challenged by two rivals.

The top US commander in Afghanistan, General Stanley McChrystal, is due to report on the situation in Afghanistan after the elections. His report will not include a request for additional troops, Defence Secretary Robert Gates said last week.

The size of the US presence will near 70,000 once Obama's previously ordered buildup is complete later this year.