Help! Got a job offer while another branch of the same company is pending


I have got a job offer from a company (A) last Thursday, which is decent. They told me I have to give them an answer by Wednesday, which is tomorrow.
However I had an interview with a branch of the same company (B) in another country the following Monday, and this position is my first choice.
I have told them upfront that I have an offer from another company with a deadline on Wednesday, and they have pushed the decision to be made by Friday- that was the best they could do as they have candidates to interview on Friday.
With this information, I asked company A if they could give me until Friday to think it over. I told them that the situation changed and I am waiting for another result- and that I don’t mean this is the second choice but I want to make a decision after I know the result so that I won’t regret later.
That was today and I’ve just been informed that the deadline cannot be changed and is not further negotiable.
This means that I have to make a decision by tomorrow- what should I do!?

I haven’t told either of them that the offer I mentioned was from another branch of the same company.

I’d really appreciate your advice, and thank you for reading!