Geneva  - While Italy hailed as "historic" its return Thursday of 227 would-be immigrants to Libya, the United Nations Refugee Agency said it was concerned that some of them were in need of international protection.

UNHCR "deeply regrets the lack of transparency surrounding the event," spokesman Ron Redmond told the German Press Agency dpa by telephone.

He said the move was a "shift in policy of the Italian government and a source of serious concern for UNHCR."

"We don't have any information available on the nationalities of the group," said Redmond, adding that it was "likely, given past experience, that among those sent back to Libya are people in need of international protection."

The group could include asylum seekers.

According to UNHCR in 2008 an estimated 75 per cent of people who arrived to Italy in these makeshift boats by sea applied for asylum and 50 per cent "were granted some form of protection."

Italy's coastguard initially intercepted the migrants, including 40 women, on Wednesday when they were found on three stranded vessels in waters between the Italian islet of Lampedusa and Malta.

Libya agreed to accept the group, after it was determined that they had set sail from the country's shores. They were sent back to North Africa on board three Italian coast-guard patrol boats.

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)