Office of Grand Ayatollah Khamenei (may Allah grant him long life):
There is no problem in conducting transactions which are permissible according to Shari'ah rules. However, interest-based transactions and taking interest from Islamic banks and financial institutes is not permissible except for when the assets of the bank belong to non-Muslims.
Office of Grand Ayatollah Makarem Shirazi (may Allah grant him long life):
Keeping in view that Turkey is an Islamic country, there is a problem in taking interest from them (Turkish banks) except for the non-Islamic banks with branches there from which taking interest and buying partnership bonds would be permissible.
Office of Grand Ayatollah Saafi Gulpaigani (may Allah grant him long life):
If you let us know about their policies or procedures, we can give you a precise answer. Generally speaking, if it is like the partnership bonds in Iran, and there is something externally against it like a company or industrial workshops, there is no problem in making investments; there is no problem in the interest received from the investment.
An answer given by Ayatollah Mahdi Hadavi Tehrani to the above question is as under: There is no difference between depositing money in Turkish state-owned banks and buying savings bonds?