A helicopter crashed during takeoff from Kandahar airfield in southern Afghanistan on Sunday, killing 16 people, NATO said.

KABUL, Afghanistan (CNN)
U.S. Marines participate in operation Saturday to push Taliban out of Herati, Afghanistan.

The aircraft was a "civilian contracted" helicopter, not a military one, NATO's International Security Assistance Force said in a statement.

The helicopter was not shot down, ISAF said, adding that the exact cause of the crash was not known.

All the dead were civilians, ISAF said. There were an additional five casualties whose condition was not known, according to the military statement.

The chopper was a Mil Mi-8 helicopter, owned by the Russian air company Vertikal-T, the Russian news agency Interfax said, citing Russia's Federal Air Transportation Agency, Rosaviatsia.

The aircraft "was on a mission to support the peacekeeping forces," an unnamed Rosaviatsia spokesman said, according to Interfax.

Separately, a U.S. military helicopter made a hard landing in eastern Afghanistan, ISAF said.
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ISAF denied the helicopter was shot down in Kunar province, but suggested the people on board were injured.

"Personnel on the aircraft were initially treated on site and evacuated to the nearest medical facility for further treatment," the ISAF statement said.

The two helicopter incidents come a day after a plane crash that killed two airmen on a U.S. Air Force F-15 Eagle in eastern Afghanistan early Saturday, the U.S. military said.

The two-man fighter went down while it was conducting military operations, Lt. Col. Reid Christopherson, said earlier.

He said he was "confident" it had not been shot down.

July has been a difficult month for coalition troops in Afghanistan, with 51 international military fatalities, the highest so far, a CNN tally of official statistics shows.