Is Zakat obligatory on money that has reached the nisab and a full year has passed while it is in another country, inaccessible due to security disturbances, despite the need for it?

The wealth for which one is responsible, in the religious sense, is that which is owed by someone in hardship or a procrastinator. In this case, its zakat (definition) is not obligatory immediately. Rather, according to the preponderant opinion, you are obligated to pay its zakat for the past years once you receive it. If you pay its zakat along with your other wealth, it will suffice for you.