It was announced earlier on Sunday that the 32-year-old had been dropped from the third Test squad to play South Africa after he had failed to provide proof that he had not sent derogatory text messages about members of the England squad to the South African players.
Pietersen said: "I am hugely disappointed that the ECB have decided not to select me.
"I had an emotional time at Headingley but I stand by every word that I have said.
"However, none of this constitutes the end of my career as an international cricketer."
Pietersen has been replaced in the England Test squad by Jonny Bairstow.