President Barack Obama is set to announce on Thursday that he will slow plans to draw down U.S. troops from Afghanistan, instead keeping the current force of 9,800 through most of 2016 before beginning to trim levels, senior administration officials said.

Under the new plan, troops will be drawn down to 5,500 starting sometime in 2017.

The decision comes after months of deliberations between Obama, Afghan leaders, Pentagon officials, commanders in the field and White House advisers about how best to continue to support Afghan forces, senior U.S. administration officials said.

"Those have been broad discussions, deep discussions, ones that have included the president's personal engagement and a number of very detailed questions from the president about our posture," an official said.

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The U.S. troops will continue to train and advise Afghan forces, and also will focus on ensuring that any remnants of al Qaeda are prevented from posing a threat to U.S. security, the officials said.

"Our mission won't change," an official said.

The U.S.-led coalition in Afghanistan ended its combat mission after 13 years of war at the end of 2014, and Afghan troops have since been in charge of the nation's security, with help from U.S. and NATO troops.

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"The Afghan government is very comfortable with this commitment. They've been indicating a desire for this commitment for some time," an official said.

Keeping 5,500 troops at four locations will cost about $14.6 billion per year, up from the estimated cost of $10 billion to keep a consolidated force at the Kabul embassy, the official said.