to purchase a property which is been collateral security i

Dear sir,

i wish to purchase a property which is mortageged in the bank as a collateral security by the seller.wright now i don't have much money and ready to pay a part from the loan amount extra sale consideration to the seller then plan to continue to pay the emi of loan by me and once it get cleared then plan to enter into sale deed. 

Kindly instruct me what procedure should be followe,