Anelka's decision, made public on his Twitter account, comes a day after it was confirmed that neither he nor the Football Association would contest the decision that he will serve a five-match suspension over the infamous 'quenelle' pose he struck when celebrating a goal against West Ham on December 28.
He has a deal at the Hawthorns that expires in the summer.
Over the course of three posts written in French on Twitter, Anelka said: ''Following talks between the club and me, propositions were made to me in order to reintegrate me into the squad under certain conditions that I cannot accept.
''Wishing to retain my integrity, I have therefore taken the decision to free myself and put an end to the contract linking me with West Bromwich Albion to 2014, with immediate effect.''
West Brom's reaction suggested Anelka's revelation had caught them by surprise.
They stated: "The club confirms it has been continuing discussions with Nicolas Anelka and his advisers as part of its own internal enquiry into the gesture he made after scoring against West Ham United on December 28.
"Following the conclusion of the FA's enquiry into the same incident, the club had hoped to conclude its own investigations next week.
"The club notes Nicolas Anelka's comments on Twitter this evening (Friday). However, the club has received nothing formally regarding the termination of Nicolas Anelka's contract from either him or his advisers.
"The club regards the release of such a statement on social media as highly unprofessional and will make a further statement when appropriate."
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