The Amsterdam-listed company stock rose more than 12 percent in early trading.

Allianz Capital Partners, AXA Investment Managers and OMERS Infrastructure were investing in the unit, Altice said, in a deal that valued the division as a whole at 3.6 billion euros.

The telecoms group, owned by billionaire Patrick Drahi, is striving to regain market confidence after a steep fall in its shareprice a year ago heightened concerns about its ability to repay its 30 billion euros of debt.

Altice has already raised some 4 billion euros in cash this year through sales of stakes in its telecoms towers businesses in France and Portugal to help reduce the debt pile.

"Through these transactions, Altice France and Altice Europe will deleverage and will have access to new and cheaper liquidity to invest in its fibre infrastructure," Drahi said in a statement. The firm reported earlier this month a sharp increase in customers in France in the third quarter, thanks to heavy promotions, and said it expects to return to growth next year.

(Reporting by Sarah White ; Editing by Matthias Blamont and Richard Lough)