In an interview with the American television network Fox News, Mark Esper warned, however, that the reduction of manpower will only be done if a series of conditions are met and if the Pentagon considers that it will be feasible to carry out missions in the region with fewer military personnel.
"Right now, we believe that we can do all the main missions and, above all, ensure that the United States is not threatened by terrorists from Afghanistan," said the US Secretary of State.
For Esper, the Afghan peace process "is not perfect", but it must continue to progress.
"It is a thorny path, it is a hard path," he admitted.
Earlier this year, the United States Government and the Taliban signed a historic peace agreement, with the aim of ending the US presence in Afghanistan.
The agreement provides for the withdrawal of US military personnel from the region in exchange for the Taliban's commitment that they will not engage in terrorist acts against the United States.
The total withdrawal of US troops from the country is one of the points of the agreement, which also includes intra-Afghan negotiations and commitments to fight terrorism. For their part, insurgents must also cut their relations with the terrorist organization Al-Qaida.
However, the process has suffered several setbacks due to mutual attacks between Taliban and Afghan troops.