The subsidiary, known as Reintel, could fetch between 1.2 billion euros and 1.3 billion euros ($1.4 billion-$1.5 billion), Expansion said, citing financial sources.

Red Electrica declined to comment, while KKR, Axa and Allianz did not immediately respond to requests for comment.

Reintel, which is owned by Red Electrica, operates a network of more than 50,000 km (31,068 miles) of fibre-optic cable laid along the electricity grid and rail network.

($1 = 0.8636 euros)

(Reporting by Nathan Allen)