After the 80 million share sale, Vodafone and TIM, which hold a 37.5% stake each in INWIT, will continue to retain joint control and an equal stake in the tower group, the two companies said in separated statements.

The shares will be placed with institutional investors through an accelerated bookbuilding process, starting immediately. Both phone carriers said they intended to use the cash proceeds from the sale to reduce their debt.

BofA Securities, Banca IMI, Goldman Sachs International and UBS are joint global coordinators of the offer.

INWIT's shares closed up 0.56% at 10.73 euros on Wednesday.

Telecom Italia and Vodafone agreed in July to fold their Italian mobile tower assets in Italy into INWIT and said they would later sell up to a combined 25% stake in the mast company.

(Reporting by Elvira Pollina, editing by Giulia Segreti and Mark Potter)