You can only purchase music from the iTunes Music Store that matches your country of residence and your billing address. Each country supports credit cards issued by banks in these countries. For example, a Visa card issued in the United States can only be used at the U.S. iTunes Music Store and so on. This is true with pre-paid cards as well.
In accordance with the contracts between Apple, the artists, and the record companies, the iTunes Music Store is available to customers who reside in the following countries: