Outgoing Defense Secretary Chuck Hagel meets with troops in Afghanistan on Sunday and explains why 1,000 more must stay. (Reuters)

Defense Secretary Chuck Hagel on Saturday confirmed that the Obama administration will leave up to 1,000 more troops than originally planned in Afghanistan beyond year’s end, as the United States and NATO nations scramble to ensure that a new international mission to support Afghan forces is launched on time.

Hagel, in his final visit to Afghanistan before stepping down as Pentagon leader, said President Obama had given the military some flexibility to cope with “any temporary force shortfall” stemming from other NATO nations’ difficulties in delivering troops on time.

“This will mean the delayed withdrawal of up to 1,000 U.S. troops — so that up to 10,800 troops, rather than 9,800, could remain in Afghanistan through the end of this year, and for the first few months in 2015,” Hagel said at a news conference alongside Afghan President Ashraf Ghani.

Officials said the delay in the NATO deployment was due to a dispute this summer over the outcome of Afghanistan’s presidential election, which in turn postponed ratification of agreements needed to keep foreign forces in the country after Dec. 31, the deadline for ending NATO’s combat mission.

Hagel said the shift in troop numbers, along with a recent White House decision to expand some authorities for remaining U.S. forces, would not alter Obama’s framework for putting an end to the U.S. role in the 13-year-long Afghan war.

Map/graphic: Afghan forces are expected to take the lead or have full responsibility for security across their country by the end of 2014.

Under a plan announced in May, the number of American troops was supposed to fall to 9,800 by Jan. 1, 2015. By the time Obama leaves office in 2017, only a small force attached to the U.S. Embassy in Kabul is to remain.

“Essentially, President Obama has just bought some time for the process to catch up,” Hagel said.

But the administration’s new plans do reflect the challenges of curtailing the U.S. military role in Afghanistan. This country is still reliant on foreign forces for air support, logisitics, intelligence and military funding to fight the ongoing insurgency.

Hagel said the slowed withdrawal, which officials have described as a “bridging solution” until the full NATO force can get in place, was initially recommended by Gen. John F. Campbell, the commander of U.S. and NATO forces in Afghanistan. NATO nations are expected to finalize their troop contributions in coming weeks.

Hagel’s visit comes less than a month before the start of the new NATO mission focused on training Afghan security forces. In addition to that program, which will include more than 12,000 U.S. and NATO service members, some U.S. troops will take part in a separate counterterrorism mission focused on al-Qaeda.

Although Afghan troops are now largely able to stage operations and repel Taliban attacks on cities, they are also suffering high casualties as they confront the Taliban, which may seek to capitalize on the departure of most foreign forces this year.

“This is going to be a threat that they continue to deal with,” Hagel said. “That’s why we and our [NATO] partners will continue to help.”

Ghani said Afghanistan is determined to ensure that the Taliban is not able to reverse the security gains of recent years. “What we strive for is normalcy,” he said.

Officials said Hagel, who served as an infantryman in Vietnam, wanted to make the trip in part to bid farewell to U.S. troops serving in Afghanistan.

The former Nebraska senator departed for Afghanistan just hours after Obama, in a White House ceremony, announced he would nominate Ashton B. Carter, a physicist who previously served as the Pentagon’s second-in-command, to replace Hagel.

Carter must be confirmed by the Senate.

Hagel’s resignation last month, with less than two years on the job, reflected the changing focus of U.S. military policy following the rise of Islamic State militants in Iraq and Syria, and the renewal of U.S. airstrikes in the Middle East.

U.S. officials say the new NATO support mission will ensure that Afghanistan doesn’t suffer the same military collapse that has occurred in Iraq over the past year.

Seth Jones, an Afghanistan expert at the Rand Corp., said the conflict in Afghanistan was far from over.

“The war’s not going to end,” Jones said. “The war is going to continue whether the United States is there or not. It’ll just transpire differently,” depending on the future of U.S. and NATO involvement.