Approximately 3,000 additional American troops have now deployed to Afghanistan under President Donald Trump's revised strategy for the war-torn country, the Pentagon said Thursday.

The Pentagon had previously put the number of U.S. forces in Afghanistan at about 11,000 but Trump in August authorized an increase requested by the commander on the ground, General John Nicholson.

"We've just completed a force flow into Afghanistan," Joint Staff Director Lieutenant General Kenneth McKenzie told Pentagon reporters.

"The new number for Afghanistan is now approximately 14,000. Might be a little above that, might be a little below that as we flex according to the mission."

The extra troops will help train and advise Afghan security forces, who are struggling to beat back a resurgent Taliban.

Nicholson has said he needs nearly 16,000 troops overall in Afghanistan, and NATO nations have pledged to help make up the difference.

Aside from additional troops, Trump's plan also comprises an open-ended U.S. troop presence in Afghanistan, where his predecessor Barack Obama had ordered a calendar-based draw-down of American forces.