A helicopter crash than killed Ghana's ministers of defence and environment - along with six other people - was caused by poor weather conditions, an investigative committee has found.

The Z9 military helicopter plummeted in a dense forest as it was flying from the capital, Accra, to the town of Obuasi in August. There were no survivors.

After a two-month probe, investigators found that the aircraft lost altitude and lift due to "downdraft", a downward current of air.

The helicopter was "airworthy", the report added, but recommended the Ghana Air Force fleet be modernised as it currently lacks modern safety and navigational systems.

For instance, the 13-year-old helicopter did not have a terrain awareness and warning system (TAWS), a device that alerts pilots to potential ground collisions, Captain Paul Forjoe, a retired commercial pilot and aviation engineer who led the investigation panel, said.

The probe was carried out by the Ghanaian authorities and US aviation experts. The investigators also received help from the helicopter's Chinese manufacturer.

On the day of the crash, the passengers were travelling to Obuasi for an event to tackle illegal mining.

The most high-profile people on the helicopter were Defence Minister Edward Omane Boamah and Environment Minister Ibrahim Murtala Muhammed.

One eyewitness told the BBC the helicopter was flying at an "unusually low altitude".

He said he heard the sound of the helicopter passing by, followed by a "loud sound" and then a "bang".

The farmer said when he got to the scene there was "no-one to be rescued".