The US plans to dramatically cut troop levels in Afghanistan as President Donald Trump reshapes America’s foreign commitments and fulfills long-standing promises to bring military forces home.

The Pentagon will withdraw 7,000 of about 14,000 troops in Afghanistan, according to a US defence official.

The decision emerged a day after Trump said he would pull US forces from Syria, a move most of his national security team had opposed for months. And it comes as Defense Secretary Jim Mattis announced plans to resign, citing differences with Trump over the value of America’s alliances and leadership in the world.

Trump has long criticised the 17-year-old war in Afghanistan, the longest military conflict in US history and one that has cost about 2,300 American lives. He only reluctantly agreed to his military advisers’ request to allow about 4,000 more troops to be sent to the country last year.

Since American troops first arrived in Afghanistan in the aftermath of the Sept 11, 2001 terror attacks, the US has appropriated about $126 billion for relief and reconstruction, including $78 billion for security, according to a July report from a Pentagon watchdog. Yet the US presence and funding couldn’t prevent conditions on the ground from deteriorating.