Norway's Telenor (TEL.OL) on Monday put up for sale an 8.1 percent stake in Amsterdam-based telecoms operator Vimpelcom (VIP.O), worth about $555 million at Friday's closing price, and said buyers would be sought through a book-building process.

Telenor also said it was considering issuing bonds worth up to $1 billion, with the option for investors to exchange their holding in the bonds into Vimpelcom shares after three years.

Telenor announced in October 2015 it aims to sell all of its 33 percent stake in Vimpelcom but has yet to find a buyer. The company last month told Reuters the sale was still in a planning phase.

Morgan Stanley and J.P. Morgan will be joint global coordinators and joint lead book-runners of the stake sale, while Citigroup and Credit Suisse will act as joint book runners, Telenor said.

"The pricing of the offering will be announced following the completion of the book building process," it added.

The offer consists of 142.5 million American depository shares (ADS) in Vimpelcom, about a quarter of Telenor's total holding in the firm. The underwriters will also get an option to buy up to 21.38 million additional ADS.

Vimpelcom in February paid $795 million to settle a U.S. and Dutch probe into a bribery scheme in Uzbekistan.

Telenor has been in open conflict with Vimpelcom's other major shareholder, Russian billionaire Mikhail Fridman, over control of Vimpelcom, to the point where it became a diplomatic issue between Oslo and Moscow.

The Norwegian state holds a 54 percent stake in Telenor.