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

The current American force in Afghanistan of 9,800 troops will remain in place through most of 2016 under the Obama administration’s revised plans, before dropping to about 5,500 at the end of next year or in early 2017, senior administration officials said.

Obama had originally planned to pull out all but a small, embassy-based U.S. military presence by the end of next year, a timeline coinciding with the final weeks of his presidency. But military leaders argued for months that the Afghans needed additional assistance and support from the U.S. to beat back a resurgent Taliban and hold onto gains made over the last 14 years of American bloodshed and billions of dollars in aid.

The White House had said a review has been underway for months and that Obama’s decision would be based on the country’s national security needs.

This is the second draw-down delay announced by Obama this year. In March, Obama said he planned to reduce U.S. forces in Afghanistan 5,500 U.S. military personnel by the end of this year, and then to an “embassy-only” presence by the end of 2016.

“The timeline for a withdrawal down to a embassy center presence, a normalization of our presence in Afghanistan, remains the end of 2016,” Obama said in a joint press conference with Ghani last March.

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.

But Afghan forces have struggled recently in assaults from Taliban militants, who briefly took over the northern city of Kunduz.

President Ashraf Ghani of Afghanistan had also pressed for Mr. Obama to keep more troops, and many in Washington who have worked closely with the Afghans over the past several years were loath for the United States to pull back just when it had an Afghan leader who has proved to be a willing partner, unlike his predecessor, Hamid Karzai.

Mr. Ghani is acutely aware of his country’s need for help from the United States and its NATO allies. The American military has repeatedly stepped in this year to aid Afghan forces battling the Taliban, launching airstrikes and at times sending Special Operations troops to join the fight, despite Mr. Obama’s declaration that the American war in Afghanistan had ended.

Obama announced the end of the Afghan war with similar fanfare last spring, saying it was time for the U.S. to “turn the page” on more than a decade of deadly conflicts. But his remarks at the time also foreshadowed the difficulties he would face in fulfilling that pledge.

Obama’s announcement is a major political reversal as he vowed to conclude the U.S. commitment in Afghanistan before he leaves office.