A direct train from Uzhgorod will go to Mariupol. This was announced by the 0629.com.ua with reference to the site of the Ukrzaliznytsya.
On March 3 at 7:00, a charter train will go from Uzhgorod to Mariupol. The travel time will be 36 hours 2 minutes, the arrival in Mariupol is on March 4 at 19.00.
Now, the tickets to Mariupol are on sale, but the train will go back empty.
According 0629.com.ua, at the railway station of Mariupol, they do not know anything about this train, although the information about it is posted on the official ticket sale site of the "Ukrzaliznytsya".