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Commuters on the Paris Metro will have to wait until 2019 for the underground rail network to be fully covered by 4G, it has been announced.

The three-year delay in the roll-out of 4G services across the entire network has been blamed on technical difficulties related to siting relay antennas, and keeping installations cool.

They also said that working overnight only to limit disruption to Metro services has also slowed progress.

The capital's public transport operator RATP currently offers 4G coverage on Metro lines 1 and 14, as well as RER lines A and B within Paris limits.

Elsewhere, 4G coverage for the Rennes Metro is expected this summer, while the Toulouse metro has been operational for four months. As for Marseille and Lyon, 4G network deployment projects are still in their early stages.