The international credit rating agency Standard&Poor's (S&P) has kept Turkey's credit rating at BB+ and outlook on negative, according to S&P's statement released on Friday evening.Meanwhile, S&P decreased Turkey's credit rating based on national currency to BBB-/A-3 and outlook on negative, citing the questions regarding Turkey's Central Bank's operational autonomy.Moody's and Fitch, other prominent credit rating agencies, have also kept their ratings and outlook stable for their first assessments of 2015.