WASHINGTON – Secretary of Defense Jim Mattis has signed orders to deploy an additional brigade-sized force to Afghanistan, two defense officials told Military Times.

Mattis authorized the deployments through the Secretary of Defense Orders Book, or SDOB, process last week and through a few earlier approvals, the officials said.

The SDOB is a biweekly process where combatant commander requests for forces are validated and sourced, then presented to the defense secretary for his approval and signature.

However, it won’t be a particular brigade deploying, the officials said. Instead it will be a total of approximately 3,500 forces from all the services, in order to add more air and ground assets to Afghanistan’s campaign against the Taliban and also to conduct operations against various terror groups in Afghanistan, including the Islamic State.

The Pentagon will work to identify units that deploy, one official said. In addition, some of the forces that will deploy already have part of their units on the ground in Afghanistan, to make those units whole, Mattis has said previously.

Earlier this month the Pentagon acknowledged that it currently has 11,000 forces on the ground, instead of the 8,500 it had previously reported.

Mattis had said that getting an accurate count of troop levels on the ground in Afghanistan was needed in order to make an informed decision on how many and what types of forces should be added.

The additional troops will bring the total of U.S. forces in Afghanistan to at least 14,500. There are likely more U.S. service members on the ground in Afghanistan than that at any given time, because the Pentagon does not include some categories of troops, such as forces rotating in as part of a relief in place, as part of the total.