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Making an unannounced visit to Kabul on Saturday, new Defense Secretary Ash Carter suggested that the United States' troop withdrawal from Afghanistan may be slowed to ensure that "progress sticks," Reuters reports.

"President Obama is considering a number of options to reinforce our support for President (Ashraf) Ghani's security strategy, including possible changes to the timeline for our drawdown of U.S. troops," Carter said on Saturday.

The current schedule would wind the number of U.S. troops in Afghanistan down to just more than 5,000 by the end of 2015, with a target of lowering that on to a "normal" troop presence at the U.S. embassy in Afghanistan by the end of 2016.