President Barack Obama is weighing several options for boosting US troop levels in Afghanistan as a debate rages in his administration over whether to persist with a counter-insurgency strategy or to narrow it to a counter-terrorism drive against al Qaeda.

"In a few weeks, I expect we will decide, in NATO, on the approach, and troop levels needed, to take our mission forward," Rasmussen told a meeting in Edinburgh of the NATO parliamentary assembly, which includes lawmakers from around the world.

In an interview with Reuters later, Rasmussen said there was a broad consensus in support of the "general thrust" of the recommendations made by the top US and NATO commander in Afghanistan, General Stanley McChrystal.

McChrystal has recommended an increase of 40,000 troops. The options being considered by Obama range from dispatching 10,000 to about 40,000 extra troops, according to a US official.