English to Italian

I am studying international relations and I notice that sometimes some countries try to give "legitimacy" to their actions by saying something to the effect that: "That was previously announced" or "That is based on a prior announcement."

For example, this might be in terms of an international agreement or contract between Party A and Party B. Party B simply makes a formal announcement that his country is no longer bound by the conditions of some international AGREEMENT.

Later, when Party A, Party C, or the representatives of other governments ask about his failure to uphold the contents of the AGGREEMENT, he says "Oh, we already made a prior announcement that we are no longer bound by that ...... "

As if to say that such an announcement gives his actions some overtones of legality ......

And of course, it could also work the other way, whereby Party B says: "We are intending to annex these islands ..... " and then when they send the military troops in to do it they say it is 100% legal because "We already made a previous announcement that we were doing that ...... "

So, of course, often it is seen that these legal principles or quasi-legal principles are rendered into Latin to give them the most scholarly appeal, but ..... because this "by prior announcement" idea is not really fully valid from a scholarly viewpoint, I thought it could more properly be rendered into something similar, which would be modern Latin, and that would be Italian.

Hence, I am wondering how to say in Italian --
by prior announcement
- OR -
by previous announcement

(Would these be different? Above, I have given the background to what I am thinking about, so please explain your translation if necessary ..... & thank you very much. )