The remarks by Esper in an interview with Reuters News Agency on Monday came on the heels of a Thanksgiving trip last week to Afghanistan by President Donald Trump, who spoke of potential troop reductions and said he believed the Taliban would agree to a ceasefire in the 18-year-old war, Al-Jazeera reported.
If honoured by all sides, a truce could lead to a significant reduction in violence. But US military commanders would still focus on the threats associated with two other armed groups in Afghanistan: the Islamic State of Iraq and the Levant (ISIL , ISIS or Daesh) and al-Qaeda.
Esper noted that the Trump administration had been discussing potential reductions in troop levels for some time, both internally and with US allies.
"I feel confident that we could reduce our numbers in Afghanistan and still ensure that place doesn't become a safe-haven for terrorists who could attack the United States," Esper said, without offering a figure.
"And our allies agree we can make reductions as well," he added.
Asked whether such reductions would necessarily be contingent on some sort of agreement with the Taliban, Esper noted, "Not necessarily". He did not elaborate.
There are currently about 13,000 US forces in Afghanistan as well as thousands of other NATO troops. US officials have stated that US troop levels could drop to 8,600 and still carry out an effective counterterrorism mission, as well as some limited advising for Afghan forces.
A draft accord agreed to on in September would have withdrawn thousands of American troops in exchange for guarantees that Afghanistan would not be used as a base for attacks on the US or its allies.
Still, many US officials privately doubt the Taliban can be relied upon to prevent al-Qaeda from again plotting attacks against the US from Afghan soil.