A bag containing a computer and two USB memory sticks holding police security plans for the Paris Olympic Games was stolen on Monday evening from a train at the capital's Gare du Nord station, police sources said Tuesday.

The bag belonged to an engineer from Paris City Hall, the police said, confirming a report by BFM television, adding that he had put the bag in the luggage compartment above his seat.

As his train was delayed, he decided to change trains at which point he discovered the theft.

The engineer said his work computer and two USB sticks contained sensitive data, in particular the municipal police's plans for securing the Olympics.

An investigation is being conducted by the regional transport police.

Paris City Hall was not able to immediately comment when contacted by AFP.

Two thousand municipal police officers will be deployed during the Games, with a total of around 35,000 security forces expected to be on duty each day for the Olympics that start on July 26.