The brothers were killed near Haska Mina district of Nangarhar province.
They slain brothers had visited their family during Eid, when the militants captured them.
The ISIS-K faithfuls also killed the soldiers' uncle.
Meanwhile, in a separate incident in the province, at least four people, including three soldiers sustained injuries after a road-side mine exploded.
The explosive was plated by militants who targeted army vehicles.
No group has claimed responsibility so far.
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