Standard & Poor's Ratings Services today assigned its 'BB-' rating to the hybrid Tier-1 securities to be issued by India's largest private sector bank - ICICI Bank.The differential between the issue rating and the counterparty credit rating on ICICI Bank reflects the subordinated nature of the notes and embedded interest deferral feature, S&P said in a statement.The proposed hybrid Tier-1 notes are perpetual noncumulative subordinated debt securities.These notes will have a call option of 10 years from the date of issue.The subordination feature reflects the payment obligation towards the securities that is junior to the claims of the senior and subordinated debt holders and senior to the claims of the prefence and equity shareholders of ICICI Bank.