The Trump administration is planning to withdraw thousands of troops from Afghanistan, US media say.
Reports, citing unnamed officials, say about 7,000 troops - roughly half the remaining US military presence in the country - could go home within months.
According to BBC, the reports come a day after the president announced the country's military withdrawal from Syria.
Earlier on Thursday, Mr Trump's Defence Secretary Jim Mattis announced his resignation from his post.
Reports about the sharp reduction of forces emerged on Thursday, but have not been confirmed by US defence officials.
Analysts have warned that a withdrawal could have a "devastating" impact and offer Taliban militants a propaganda victory.
The Taliban - a hardline Islamist movement that carries out frequent suicide bombings and attacks against government and military targets - is active in much of Afghanistan.
They ruled Afghanistan from 1996-2001, imposing a brutal version of Sharia law, including public executions and amputations, and banned women from public life.