Luctuosissimi eventus, issued October 28, 1956, is an encyclical of Pope Pius XII urging public prayers for peace and freedom for the people of Hungary.
The Pope is "deeply moved by the sorrowful events which have befallen the people of Eastern Europe and especially of our beloved Hungary, which is now being soaked in blood by a shocking massacre. And not only is our heart moved, but so too are the hearts of all men who cherish the rights of civil society, the dignity of man, and the liberty which is due to individuals and to nations".
More information on the Wikipedia page [1]: the Hungarian Wikipedia page is [2].