There was no diplomatic infrastructure for the UN to become involved to intervene. There were also no nuclear treaties at the time, so neither the US r UN could use treaty abrogration to justify a military intervention under international law at that time.

Then, just like now, the leaders of the countries involved were simply playing a dangerous game of military chicken.

I'm not sure when the IAEA came into being, but I'm 99.9% certain that there was no infrastructure for inspections then, as there is now, because there were only "us and them" as nuclear powers at the time. It is certain the US would never allow, not then, not now, any foreign or international inspecitions of our nuclear programs.

As to sanctions against Cuba, the US had had an embargo against Cuba since the time you speak of Gareth, and the Bush administration is currently "strengthening" it because so many US businesses, not to mention the European ones, are now operating in Cuba.

Just another way for Bush to buy votes in the Florida Cuban exile community for the 2004 election.