Fact scenario:

Current UN Secretary-General Antonio Guterres is a national of Portugal. He recently conducted an official visit to Ottawa. In a rather unusual development - demonstrating a surprising degree of local knowledge - he ran over to a parked OCTranspo train and scribbled on it with black marker, writing "public transportation is very important and this should really have been fixed by now". [In case you are working remotely, Minister Garneau notes that the entire Ottawa light-rail system has not been working for almost a month now.]

Immediately thereafter Mr. Guterres stated publicly, "what I've done was clearly an internationally unlawful act, for which there is absolutely no lawful excuse. To be honest with you, I just couldn't help myself. Good public transportation is just so important."

Assuming that what Mr. Guterres did was an internationally unlawful act - and, frankly, that might be disputed - the Minister would like to ask for compensation for the damage done to "that beautiful albeit quite useless train". That said, he is uncertain whether to ask for this from the United Nations or Portugal or, possibly, both ("just to be safe").

What legal advice can you provide Minister Garneau to help guide this decision?