Diego Costa
Costa happy at having taken up a new challenge at ChelseaReuters

Chelsea have officially announced the signing of Atletico Madrid striker Diego Costa on a five year contract for a reported £32 million.

The Blues, who had earlier revealed they had reached an agreement with the La Liga champions over the transfer fee of Costa, confirmed the news on their official website on Tuesday.

"Chelsea Football Club is delighted to announce Diego Costa has today completed his transfer from Atletico Madrid by signing a five-year contract," read a statement.

"He will join up with the first team for our preseason European training camp next week."

The 25-year-old striker, who was not able to make an impact in the 2014 World Cup following Spain's premature exit from the group stages, expressed his delight at having signed for Chelsea.

"I am very happy to sign for Chelsea," said Costa. "Everybody knows it is a big club in a very competitive league, and I am very excited to get started in England with a fantastic coach and teammates. Having played against Chelsea last season I know the high quality of the squad I am joining."

The Brazil-born striker also thanked everyone at his former club Atletico, saying the team played a big hand in his development.

"I would like to thank everybody at Atletico who made me into the player I am, it was an incredible time for me, but now I am starting a new adventure and I hope to win many trophies with Chelsea," he added.

Costa, who arrived at the Vicente Calderón from Valladolid for an undisclosed fee in the summer of 2010, enjoyed an excellent season with Atletico Madrid last season, helping the Los Rojiblancos lift their first La Liga title since 1996 by scoring 27 goals from 35 league appearances.

Meanwhile Chelsea have reportedly agreed to sell their Senegalese striker Demba Ba to Turkish club Besiktas for a fee of around £8 million.

Besiktas president Fikret Orman claimed he has successfully negotiated a deal with the Blues over the transfer of the 29-year-old striker.

"Demba Ba is an excellent player. We have been in talks with Chelsea for a long time over bringing him to Istanbul. Talks are ongoing. Chelsea initially wanted £10 million for Ba but we have negotiated a price we are happy with. We'll tell the media once the final deal is done," said Orman, according to the Daily Mail.

The former Newcastle striker, who had earlier claimed that manager Jose Mourinho had convinced him to continue at Chelsea for another season, will be glad to make a move out of Stamford Bridge as he only made a handful of appearances for the Blues last season.