The U.S. will withdraw 500 troops from Iraq and 2,000 from Afghanistan before President Donald Trump leaves office, leaving around 2,500 soldiers in each country, Acting Secretary of Defense Chris Miller has announced.

In a press briefing on Tuesday, Miller said the troop withdrawals will take place before January 15, 2021.

"I celebrate this day as we continue the president's consistent progress in completing the mission we began two decades ago," Miller told reporters, adding that the withdrawal decision was a "collaborative" one between Trump and senior US military leaders.