'We're going to do that with a clear eye not only on the needs in Afghanistan, but also the needs of the force in general and on our other security commitments around the globe,' Mullen said.

But he noted that how to use the increased troops in Afghanistan is more important than the numbers of troops needed since 'time is not on our side' there.

Feeling a sense of urgency, the US has to regain the initiatives and start to turn the security situation in Afghanistan around in the next 12 to 18 months, he added.

President Obama announced a new strategy for Afghanistan and Pakistan in March, which combines military, civil and diplomatic approaches, in a bid to disrupt, dismantle and defeat Al Qaeda and other terror groups.

Gates had ordered a report from McChrystal on the assessment of the security situation in the country and how to implement President Obama's strategy in 60 days after he took over the command.