UPDATE 1-France's Orange to sell entire 2.5% stake in Britain's BT

(Adds details on placement)

June 27 (Reuters) - BT Group said on Thursday that Orange, France's number one telecoms operator, would offer up its entire 2.5% stake in Britain's former telecoms monopoly.

BT said it intends to repurchase up to 80 million pounds of shares after Orange said it would offer about 248 million shares in BT to institutional investors by means of an accelerated bookbuild offering.

At closing prices, the 2.5% stake is worth 493 million pounds, or around 550 million euros, according to a Reuters calculation.

"Following the offering, Orange will no longer be shareholder of BT and will no longer have any exposure to the shares of BT, having recently fully hedged its exchangeable bonds into BT shares issued in June 2017, Orange said in a separate statement.

BT said it intends to hold the shares acquired in the repurchase in treasury, adding that the offer price and final number of shares sold will be determined by Orange at the conclusion of the bookbuilding process.

"The repurchase is expected to settle on 2 July 2019," BT said.

Citigroup Global Markets Limited is acting as sole bookrunner for the share placement, the companies said. (Reporting by Justin George Varghese and Sarah White; editing by David Evans)