Faulty maintenance on a signal and hot weather may have played a role in a collision between two trains in south-west France in which 25 people were injured, the country's transport chief has said.

France, whose extensive train network is widely used by tourists in summer, is upgrading railways nationwide as part of larger reforms of the industry.

A regional train crashed into the back of a slower-moving national TGV train bound for Paris in the town of Deguin yesterday evening.

Frederic Cuvillier said on Europe-1 radio today that "maintenance on the signals appears to have been disrupted and faulty".

He noted that heat can also cause signal problems. He would not say whether the accident was due to human error or technical problems.

Nine of the casualties were seriously injured, authorities said.

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