Is it permissible to mortgage foreign currency or gold as a deposit for a loan, equivalent to its value, to purchase a house, when the bank increases the amount by what is called loan interest?

Lending with interest is prohibited; it is usury (riba), and it is forbidden by consensus, whether or not it is accompanied by a pledge, due to Allah's saying: ﴿O you who have believed, fear Allah and give up what remains [due to you] of riba﴾, and the saying of the Messenger of Allah, peace and blessings be upon him: "Allah has cursed the one who consumes usury and the one who feeds it to others." It is permissible to pledge money and gold if the pledgee does not use them. However, if the pledgee uses them, it is a stratagem for usury. Similarly, it is forbidden to place money in an interest-bearing investment account or an investment deposit in usurious banks, because it is a forbidden usurious loan. As for some "Islamic" banks that involve the client in Tawarruq and Murabaha in "international metals" with a deposit guarantee, there are two prohibitions involved: the prohibition of Tawarruq in international metals, and the prohibition of investing deposits in them if their transactions are not regulated and they deal with prohibited Tawarruq.