The 27-year-old moves to the Potters after four years with the Royals where he was a mainstay of the squad that claimed promotion to the Premier League, although his appearances in their two-year stay in the top flight were restricted by injury.

The deal will initially cost the newly-promoted club £2million potentially rising to £2.25million.

Stoke chief executive Tony Scholes told the club's official website: "We are delighted to make Ibrahima the club's latest signing.

"He is a quality addition to the squad and comes with plenty of Premier League experience having played in the top flight with Reading."

Sonko made 122 league starts for the Royals following his transfer from Brentford and quickly established himself at the heart of their central defence.

Sonko has captained Senegal Under-23s but is still eligible to play for France - where he lived from the age of six months - because his only appearance for the Senegal senior side came in an unofficial friendly.

Reading director of football Nick Hammond told the club's official website: "Ibrahima Sonko has been a terrific performer in the club's recent development.

"But centre-half is a particularly strong position for us in terms of both quality and quantity, especially with the continuing emergence of Alex Pearce, who adds to the experience offered by Ivar Ingimarsson, Michael Duberry and Andre Bikey.

"Bearing that in mind, we felt the timing is right for this deal and it is probably a good time for Ibrahima to seek a fresh challenge."

Sonko is Stoke's seventh signing of the summer and follows fellow ex-Royal Dave Kitson to the Britannia Stadium, as well as Seyi Olofinjana, Thomas Sorensen, Abdoulaye Faye, Andrew Davies and Amdy Faye.

And the Potters are not expected to stop their spending there, with a bid for Joe Ledley already lodged and a move for Jon Walters still likely.

Cardiff chairman Peter Ridsdale has rejected the Potters' initial £5million offer for Ledley but the club are still in financial difficulty and could be prepared to do business at a higher price. Everton have also been linked with the 21-year-old but have not as of yet made an offer.

Walters, meanwhile, looks set to end one of summer's longest transfer sagas by moving to the Britannia Stadium before Monday's deadline. He is reported to have put in a transfer request at Ipswich and should complete a move back to the north-west over the weekend.

City has also been linked with West Ham striker Carlton Cole and Manchester City duo Gelson Fernandes and Javier Garrido in Friday's press.