Barack Obama could use an unusual war council session to make his long-awaited decision on whether to commit tens of thousands of new US forces to the stalemated conflict in Afghanistan.

Military officials and others said they expected Mr Obama to settle on a middle-ground option that would deploy an eventual 32,000 to 35,000 US forces to the eight-year-old conflict.

That rough figure has stood as the most likely option since before the US president's last large war council meeting this month, when he told military planners to rearrange the timing and make-up of some of the deployments.

The president has said with increasing frequency in recent days that a big piece of the rethinking of options that he ordered had to do with building an exit strategy into the announcement, revising the options presented to him to clarify when US troops would turn over responsibility to the Afghan government and under what conditions.

White House press secretary Robert Gibbs said it was "not just how we get people there, but what's the strategy for getting them out".

The presidential spokesman said it was possible Mr Obama could lock in a decision at the meeting or that it could come "over the course of the next several days".

In either case, it would not be announced this week, he said.