* Up to 500 migrants packed onto small boat from Libya
* Passengers burned sheet to attract rescue, starting fire
* Italian minister says passengers were Eritrean, Somali
* UN, pope concerned about perilous migrant traffic (Adds quotes from interior minister)
By Wladimir Pantaleone
PALERMO, Italy, Oct 3 (Reuters) - At least 94 people died and up to 250 were missing after a boat ...