Vatican City - Italy's decision to return a group of would- be immigrants to Libya "violates international norms on the rights of refugees," a top Vatican official said Friday.

Monsignor Agostino Marchetto, secretary of the Holy See's department for migration issues, made the remarks in an interview with the ANSA news agency.

He was referring to the deportation on Thursday to Libya, of over 200 migrants intercepted by Italy's coast-guard in waters between the Italian islet of Lampedusa and Malta.

The decision by Libya to accept the migrants after it was determined that they had set sail from the North African country, has been hailed as "historic" by Italian Interior Minister Roberto Maroni.

But humanitarian groups condemned Italy for failing to first establish whether among the group, were people escaping from persecution and thus eligible to enter Italy with refugee status.

A United Nations Refugee Agency, UNHCR, spokesman said it "deeply regretted" the lack of transparency surrounding the event and was "seriously concerned" by the situation.

Despite "complications" in determining the conditions from which migrants were fleeing, all of them should be treated as "presumed refugees," unless verified differently, Marchetto told ANSA.

"The treatment of those taken to Libya must also be verified," an official of Italy's Catholic Bishops Conference, Giandomenico Gnesotto said Friday, specifying that Tripoli was not a signatory of international human rights declarations.

Italy has been calling on Libya to play a more co-operative role in curbing illegal immigration across the Mediterranean.

Some 36,000 migrants arrived in Italy by sea in 2008, with around 30,000 landing on Lampedusa.

An agreement between Rome and Tripoli to begin joint naval patrols in Libyan waters is scheduled become operational next week. (dpa)