Air France said Tuesday it had filed a complaint after gold bars worth around 1.6 million euros ($2.1 million) were stolen from a plane bound for Zurich from Paris.

"We hope the investigations will allow us to quickly determine the sequence of events and identify those responsible," a spokesman said.

The gold bars, weighing around 50 kilos (110 pounds), were placed inside the plane at Paris's Charles-de-Gaulle airport last Thursday by employees of the US security firm Brink's.

It is as yet unclear how the theft happened, but an airport source said the robbers had "probably made use of airport accomplices."

This kind of shipment takes place every day, and Brink's employees always stay on the tarmac until the plane takes off.

In a separate case also involving Air France, police earlier this month made a record haul of 1.3 tonnes of pure cocaine found in 30 suitcases on board a flight from the Venezuelan capital Caracas to Paris.