A top US general has recommended a little less than 14,000 troops be present in the war-torn Afghanistan while Afghan forces take charge of the country's security.

Responding to a question from senator John McCain, US central command commander general James Mattis said the decision pertaining to US forces in Afghanistan post 2014 had not been finalised yet and he had recommended for 13,600 US troops to be present in the country following the pullout of troops in 2014.

"(The post-2014 force) that decision I know has not been made yet. It's still under consideration. I have made my recommendation. That recommendation is for 13,600 US forces," Mattis said.

He was speaking at the members of the powerful Senate Armed Services Committee during a Congressional hearing.

He said no decision has been made on the number of Nato troops in Afghanistan after 2014, but his expectation is that would be 50% of the US forces.

Testifying before the Congressional committee, Mattis said the Afghan campaign is on track.