The U.S. military says it has found no wrongful actions by personnel involved the mission of a Chinook helicopter shot down in Afghanistan in August, killing all 38 people on board.

An official investigation report released Thursday also said the chopper, which crashed in Afghanistan's Wardak province on August 6, was downed by a rocket-propelled grenade.

The 38 people killed included members of the elite U.S. Navy SEALs, along with seven Afghan soldiers and an Afghan interpreter. It was the largest loss of American life in a single day in the decade-long war.

The troops killed were flying into Wardak's Tangi Valley to assist forces targeting a Taliban leader.

In its inquiry, the U.S. military said it found the decision to load all of the personnel onto one helicopter was “tactically sound” to mitigate aircraft exposure to ground fire.

The report also dismissed speculation the helicopter had flown into a trap set by Taliban militants. It says the shootdown was the result of “the enemy being at a heightened state of alert” due to the three-and-a-half hour coalition air operation in the area.

The probe found that the special operations task force commander did not reallocate the intelligence, surveillance and reconnaissance aircraft to ensure surveillance coverage for the ongoing mission.

The U.S. military said the aircraft plummeted into a dry creek bed and was engulfed in flames after the grenade hit the chopper's rotor blade.

Separately, NATO said bomb attacks killed two of its service members in Afghanistan's south and east on Thursday.