The US will keep 9,800 troops in Afghanistan throughout 2015, delaying plans for a gradual withdrawal, the White House has said.
The US and Afghanistan announced the change ahead of a press conference in Washington between President Barack Obama and President Ashraf Ghani.
Despite ongoing security issues there, Mr Obama has promised to end America’s longest war by the end of his term.
The US will now leave a small force at the US embassy by the end of 2016.
Originally, officials planned to cut the US troop presence to 5,500 by the end of 2015.
The leaders discussed troop numbers over a working lunch and in meetings, before the press conference on Tuesday.
But with the prospect of a tough spring fighting season on the horizon, Islamic State militants trying to recruit on Afghan soil and other security concerns, officials are predicting the US will probably leave 9,800 American troops in the country long into next year.
US bases in Jalalabad and Kandahar, the Taliban capital until 2001, are central to the discussions.
President Ghani had requested that those bases remain open as long as possible.
The lunch and meetings came just as gunmen killed at least 13 people in eastern Afghanistan overnight and, separately, a suspected US drone strike near the Afghan-Pakistani border killed nine militants.
However, Mr Ghani’s presidency is a welcome change in the eyes of the White House, whose relationship with his predecessor grew increasingly strained in recent years.
When he assumed office, Mr Ghani, who lived in the US for more than a decade, almost immediately signed a security deal with American officials to keep US troops in the country beyond 2014.
The refusal of the previous Afghan administration, led by Hamid Karzai, to sign the agreement generated consternation at the White House.
By contrast, Mr Ghani has made clear his appreciation for US support, which has included more than $60bn (£40.37bn) being invested in his country’s military so far.
“We do not now ask what the United States can do for us,” President Ghani said as he opened his US visit, invoking a quote by former US President John F Kennedy. “We want to say what Afghanistan will do for itself and for the world.”
Ahead of the meetings, activist groups were calling on the leaders to make human rights a top priority.
“Both the US and Afghan governments have a legacy of human rights violations to address, from abusive militias in Afghanistan to the mistreatment of detainees at Bagram and Guantanamo,” Human Rights Watch said in a statement.
After a controversial election with disputed results, President Ghani agreed to share power with his main political rival, Abdullah Abdullah, who has taken the title of Chief Executive Officer of the country.
Six months into their term, the two leaders have made the trip to the US together in an effort to project unity, despite being unable to build a full cabinet.
In a ceremony at the Pentagon on Monday, Mr Ghani paid tribute to US soldiers who had fought in Afghanistan and thanked the US for its support.
“Each one of you has left a legacy,” he said, noting that more than 2,200 Americans lost their lives and 20,000 were wounded in the conflict.