President Barack Obama plans to keep 5,500 U.S. troops across Afghanistan into 2017, senior administration officials told NBC News — well more than the small security force he promised last year.

The United States currently has about 9,800 troops in Afghanistan — sharply down from 100,000 that were in the country as recently as 2010. Obama said last year that he wanted to withdraw nearly all of them by the end of 2016, leaving only about 1,000 to provide security for the U.S. Embassy in Kabul.

The president is expected to make a formal announcement sometime Thursday morning that he plans to maintain 5,500 troops at bases in Bagram, Jalalabad and Kandahar into 2017 and the term of his successor, the U.S. officials said Wednesday night.

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Obama reconsidered after a months-long review of U.S. policy in the region, which has included regular discussions with top Afghan leaders, including President Ashraf Ghani, one of the officials said.

The larger contingent of troops will have the same "limited mission," the officials said: counterterrorism activities against al-Qaeda and its affiliates, along with training Afghan personnel to make sure Washington has a "capable partner." They said it would cost $14.6 billion to keep the larger force in the country, while Obama's original Kabul-only presence would have cost about $10 billion.

Related: Will Taliban Invasion Keep U.S. Boots on the Ground in Afghanistan?

Afghan forces have been battling to retake the northern city of Kunduz from the Taliban since Sept. 28, but the U.S. officials denied that the recent surge of violence drove Obama's decision, saying the plan has been under consideration for months.

Defense Secretary Ashton Carter may have signaled the change in strategy last week when he asked allies in the NATO force in Afghanistan "to remain flexible and to consider the possibility of making adjustments."

In testimony before the Senate Armed Services Committee last week, Army Gen. John Campbell, the top U.S. commander in Afghanistan, said "a lot has happened" since Obama announced his drawdown strategy last year.

"Based on conditions on the ground, I do believe we have to provide senior leaders with options," Campbell said. He didn't give any numbers, but before he before he stepped down as chairman of the Joint Chiefs of Staff last month, Gen. Martin Dempsey had proposed that the United States keep more than 5,000 troops in Afghanistan.