** Ukraine's biggest mobile operator Kyivstar's KYIV.O shares fall 4.5% to $12.02 premarket

** Certain existing Kyivstar shareholders set to sell 12.5 million shares in a public offering, according to prospectus

** Parent VEON is selling 12.1 million shares while Cohen Circle is offloading 400,000 shares

** KYIV went public in New York last year after merger with Betsy Cohen's special purpose acquisition company Cohen Circle Acquisition Corp I

** VEON has 89.6% stake in KYIV, while Cohen Circle owns 7.4%

** Morgan Stanley, Barclays, Cantor and Rothschild & Co are joint book-running managers for offering

** All five brokerages covering the stock rate "buy" or higher; median PT $17 - data compiled by LSEG

** KYIV stock down 3% so far this month

(Reporting by Arasu Kannagi Basil in Bengaluru)

((ArasuKannagi.Basil@thomsonreuters.com;))