A statement from US Forces Afghanistan Command in Kabul said the service member had died of wounds sustained during operations in Logar, the eastern province where another service member was killed last week after a helicopter crash.
"Despite this tragic event, we remain steadfast in our commitment to the Afghan people and to support them in our mutual fight against terrorism," Gen John Nicholson, the top US commander in Afghanistan said in the statement.
The latest death comes after President Donald Trump ordered a boost in the number of US troops assisting Afghan forces against the Taliban as part of a new strategy to try to break the stalemate with the insurgents.
Although, most US troops are not in combat, the new strategy will give them greater authority to engage the Taliban and will involve some acting as advisers at brigade and battalion level, bringing them much closer to the front line.
Up to Aug 23, 10 US service members had been killed in Afghanistan this year, according to figures published last week by the congressional watchdog SIGAR, more than double the number killed in the same periods in 2015 and 2016.
Separately, the US military said it was investigating reports of civilian casualties caused during a combined operation in the northern city of Kunduz on Friday and was assessing the facts surrounding the incident.
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