By Andrés González and Pamela Barbaglia

Under the deal, which is being finalised, KKR will use its infrastructure fund to take a minority interest in Altice's towers subsidiary in France, the sources said.

The U.S. buyout group has trumped rival bids from private equity firm Blackstone and a consortium led by the infrastructure investment arms of insurers Allianz and Axa which also made it to the final stages of the auction, the sources said.

KKR declined to comment while Altice and the other bidders were not immediately available for comment.

Altice, whose debt equals more than twice its annual revenues, is rushing to finalize a series of non-core disposals involving telecoms towers in France and Portugal and its entire operations in the Dominican Republic.

Its founder Patrick Drahi has pledged to shift the company's focus from large acquisitions to sales growth and debt management.

The group's French masts could be valued at about 4 billion euros, according to estimates by RBC analysts, representing a multiple of 20 times its core earnings.

Altice's SFR division has around 20,000 tower sites in France although some of these assets belong to a joint venture platform with French mobile firm Bouygues.

The tower auction, which kicked off earlier this year, attracted interest from several heavyweight investors with Allianz and Axa joining a consortium with Digital Colony and Abu Dhabi Investment Authority, the sources said.

For KKR this is not the first minority deal in the telecom towers industry. Last year, it bought a 40 percent stake in Telefonica's telecom masts subsidiary Telxius for 1.3 billion euros.

As part of the Telxius deal, KKR also gained significant exposure to an international network with approximately 65,000 kilometers of submarine fiber optic cables.

Altice's reorganization, which involves the spin off of Altice's U.S. arm, is expected to complete toward the end of June and proceeds from the various auctions will be used to cut debt which rose to around $60 billion following a series of big ticket deals.

In the United States, Drahi spent $28 billion in 2015 to buy cable companies Suddenlink and Cablevision, and even flirted with a $185 billion bid for cable giant Charter.

(Additional reporting by Mathieu Rosemain in Paris. Editing by Jane Merriman)

By Andrés González and Pamela Barbaglia