US President Barack Obama said last week that he had not yet made any decision on sending additional US troops to Afghanistan, despite some calls for more resources from military commanders. White House spokesman Robert Gibbs said the situation in Afghanistan was still being evaluated.

'No resource request has come, and I don't anticipate that it will come for a little bit because there's an assessment that's ongoing about where we are right now,' Gibbs said.

US public support for the war has fallen in recent months, and Obama is facing opposition from some members of his centre-left Democratic Party to sending additional troops to Afghanistan.