Is it permissible to open a savings account in a bank to issue a letter of guarantee and pay the expenses of the letter from the interest of this account, without the company taking any amount from the interest?

It is not permissible to open a savings account in an interest-based (usurious) bank except out of necessity. It is also not permissible to enter into a letter of guarantee contract with an interest-based bank, because it charges a percentage for issuing it, which varies according to the debt and term, and these are not administrative fees as claimed. Therefore, it is not permissible to obtain a letter of guarantee from an interest-based bank unless the contract is free from prohibited elements, the person needs it, and there is no Islamic bank that can provide it.