US President Barack Obama has secretly signed an order which allows US troops to be involved in combat operations in Afghanistan throughout 2015.

US President Barack Obama has secretly signed an order which allows US troops to be involved in combat operations in Afghanistan throughout 2015.

The order will authorize American forces to continue their missions against the Taliban and other militant groups, the New York Times reported on Friday.

The new order also allows for air support - from US jets, bombers and drones - for Afghan combat missions, according to the report,.

The Times said an administration official said American forces would not carry out "offensive missions" against the Taliban in 2015.

“We will no longer target belligerents solely because they are members of the Taliban,” the official said. “To the extent that Taliban members directly threaten the United States and coalition forces in Afghanistan or provide direct support to Al Qaeda, however, we will take appropriate measures to keep Americans safe.”

Obama’s new decision has been made in recent weeks with his top national security advisors.

Previously, the president had said US-led NATO combat operations would finish at the end of this year.

The NATO follow up mission, to take over on January 1 with 9,800 US troops and about 3,000 soldiers from Germany, Italy and other member nations, was to focus on supporting Afghan forces as they take on the Taliban, in parallel with US counter-terrorism operations.