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, www.stokecity.co.uk: "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."

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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, www.readingfc.co.uk: "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.

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Earlier, midfielder Anthony Pulis signed a two-year contract with Coca-Cola Championship side Southampton after moving to St Mary's on a free transfer.

The 24-year-old had been with the Potters for three-and-a-half years since signing from Portsmouth in December 2004 but his first-team chances had been limited and he was sent out on loan to a number of clubs.

Pulis did not start a league game and spent spells with Torquay, Plymouth, Grimsby and Bristol Rovers.

Pulis - the son of Stoke manager Tony - agreed a two-year deal with the Saints with the option of a third and becomes the second player involved in a transaction between the two clubs this summer following Davies' decision to join the Potters.

Assistant manager Dave Kemp believes the move is a fresh start for the player.

He told the club's official website, www.stokecityfc.co.uk: "He's a great lad, he's been very popular here but obviously it's difficult when your father is the manager.

"It is a great opportunity for him to push on with his own career and everyone at the club wishes him all the best as he embarks on an exciting new challenge with Southampton."