Thank you, your answer might be correct when using block ciphers, however, when using AES CTR I think Maarten Bodewes' answer is the only correct one.

You are right, it prescribes ECB. This would make me even more reluctant to adhere to the standard, as ECB should be a no-go (at least that's what I thought).

I'm gonna purchase 9564-2. However, 9564-2 dates from 2014, and the amendment to 9564-1 (which added format 4 to make it easier to use with AES encryption algorithms) dates from 2015. Btw, isn't ECB pretty insecure?

It is very clear, actually. Thank you for the explanation!

Yes, that's why I do not understand the sentence "Prefixing a (16 byte) random IV however does make sense", or did you not mean anything with it specifically?

Partially: why would it make sense to do that in AES-CTR? As you explain in the other paragraphs, this IV will then just be XOR'ed with the key stream. If we assume that the key stream is based on the key and the IV, and that the IV is sent along with the cipher text, what would be the sense of prefixing the IV with the plain text?

Thanks for your answer. I don't fully get your last paragraph: it seems to contradict the other paragraphs. Prefixing/appending an IV might make sense in AES-CBC, but it won't probably make any sense when using AES-CTR. That is clear. However, in the last paragraph you seem to suggest that prefixing a random value does make sense, or do you mean 'adding' instead of 'prefixing'?