Italian authorities have been sending unaccompanied migrant children and asylum seekers back to Greece instead of considering their desire to apply for sanctuary or determining their best interests, according to a report.

New York-based Human Rights Watch have interviewed 29 children and adults who were summarily returned to Greece from the Italian ports of Ancona, Bari, Brindisi and Venice in violation of the legal framework.

Italian and international legislation states that authorities should determine what is the unaccompanied children's best interests, instead of simply removing them. However 13 of the children interviewed said they were returned to Greece without having access to a guardian or social services, in direct contravention of this legislation.

These children, along with asylum seekers, face law enforcement abuse, degrading conditions of detentions and Golden Dawn-style xenophobic assaults in Greece, according to HRW.

It is difficult to define how many migrants have been affected, according to the report. In Bari, southern Italy, almost 900 migrants trying to enter Italy were intercepted between January 2011 and June 2012 and just 12 were allowed to remain.

"Every year hundreds of people risk life and limb hiding in or under trucks and cars on ferries crossing the Adriatic Sea," said Judith Sunderland, senior Western Europe researcher at Human Rights Watch.

"Too often Italy sends them straight back to Greece despite appalling conditions and treatment there."

Most of the children were Afghan boys fleeing extreme poverty and conflict in their home country, the report said. Some migrants were sent back to Greece without being given the opportunity to lodge asylum claims.

"Some asylum seekers may not want to apply for asylum in Italy, even if given the chance, because they are convinced that their prospects for protection and integration are better in other European countries," Sunderland said. "But those who do want to apply for asylum should not be turned away."

The UN's Commissioner for Refugees in Italy, Federico Fossi, has told the New York Times that the assistance services for migrants arriving in Italy following a perilous journey on the Adriatic Sea is "discontinuous and inadequate".