US forces have reportedly conducted air strikes against Taliban troops in southern Afghanistan, days after President Barack Obama allowed expanded air strikes against the militant group.

The recent decision to expand military authorities in Afghanistan comes as the Taliban has made significant gains over the past year.

Obama relaxed restrictions on airstrikes and on ground combat, allowing US forces to support Afghan forces in their fight against the Taliban.

US personnel, who have been in an advisory role since last year, were previously allowed to attack Taliban targets for defensive reasons, or to use air strikes to protect Afghan troops, AFP reported.

"Nearly 9,800 US personnel will continue to be deployed in Afghanistan."

The AFP quoted Pentagon press secretary Peter Cook as saying: "There have been operations carried out with these new authorities.

"It’s fair to say that these strikes did target Taliban positions."

Over 5,000 Afghan security forces were killed last year alone, according to the news agency.

Nearly 9,800 US personnel will continue to be deployed in Afghanistan. The number of US military personnel is expected to come down to 5,500 by the end of this year.