The Rev. Mussie Zerai, chief of the Habeshia Agency for Development Cooperation, a refugee agency based at the Vatican, said human traffickers are torturing the 400 victims and making them raise ransoms up to $10,000, the BBC reported Friday.
"Many, many, many times I have talked with the Egyptian ambassador here in Italy," to no avail, he said.
The priest said hostages have told him by phone they are being kept in shipping containers or pits by Bedouin smuggling gangs.
Most of the migrants are trying to reach Israel, and the Physicians for Human Rights group there has documented the torture of 300 other Eritrean survivors.
Zerai said the refugees are being tortured with electric prods, others are raped and two died this week.
"We ask the European Parliament to put pressure on governments in the region to secure the release of these hostages and put an end to trafficking in human beings," he said.