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A total of 44 Afghan troops have gone missing in the US since January 2015, Pentagon spokesman Adam Stump told Reuters.
Since September alone, eight Afghan troops have left military bases without authorization, Stump said.
"The Defense Department is assessing ways to strengthen eligibility criteria for training in ways that will reduce the likelihood of an individual Afghan willingly absconding from training in the US and going AWOL (absent without leave)," Stump said.
Afghans in the US training program are vetted to ensure they are not affiliated with militant groups and have not participated in human rights abuses before being allowed into the country, he added.
The US has spent more than $60 billion to train and equip Afghan troops since 2002, but security remains precarious.
The Taliban has seized a number of districts in Helmand, Baghlan and Takhar provinces in recent months.
Experts said the troops leaving are mainly due to low morale and insufficient training to fight the Taliban militant group, in addition to a lack of economic opportunities in the impoverished country.
The US and its allies invaded Afghanistan on October 7, 2001 as part of Washington’s so-called war on terror.
The US-led combat mission in Afghanistan ended on December 31, 2014. However, at least 13,500 foreign forces, including 8,400 troops from the United States, have remained in Afghanistan in what the US is calling a support mission.