On his second day in Afghanistan, Carter flew to Kandahar from Kabul, the capital, where he had held a series of talks with Afghan government leaders and American military commanders.
Carter is in Kandahar today to receive briefings from US and Afghan commanders on progress in training Afghan security forces.
Kandahar is home to the Afghan Army's 205th Corps, elements of which are involved in a major offensive against the Taliban in neighbouring Helmand province.
Under the Obama administration's exit plan for Afghanistan, the US military presence at Kandahar will close down this year.
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President Barack Obama, however, is considering changes to the plan, including the possibility of keeping Kandahar open longer while keeping more US troops in Afghanistan this year and next than presently planned.
An Obama decision may come as early as next month when he hosts Afghan President Ashraf Ghani at the White House.
Kandahar is one of several "hubs" around Afghanistan where US troops are training and advising Afghan security forces.