He noted that "the stronger the Afghan security forces become, the less we will have to do."
The US President also vowed to change the country's approach to dealing with Pakistan, promising to crack down on Pakistan's harbouring of terrorist and militant groups.
Trump promised that Pakistan has "much to gain" from partnering with the US, but also warned "it has much to lose by continuing to harbour criminals and terrorists."
"They are housing the very terrorists we are fighting," Trump said, noting that the US gives Pakistan billions of dollars.
"That will have to change and that will change immediately. No partnership can survive a country's harbouring of terrorists."
Trump also said the US would pressure India to increase its support for Afghan economic development.
Trump's plan involves a modest increase of several thousand troops.
According to Pentagon, additional troops, above current levels of about 8,500, would serve very specific purposes, including boosting training, capacity-building and allowing advisers to work more closely with Afghan soldiers along the front lines.
The increase was effectively approved in June, when Trump gave Defence Secretary James Mattis the go-ahead to boost levels by as many as 3,900 troops.
US commanders would bring in additional advisers to support Afghan special forces, the Afghan air force and the Afghan army and police professional schools, such as the infantry and artillery schools, the report said.