A rescue operation in which an Italian towboat rescued more than 100 migrants and returned them to Libya earlier this week may have been in breach of international law, the United Nations said yesterday.

According to Spanish charity Proactiva Open Arms, an Italian towboat rescued 108 migrants from international waters on Monday and took them to Libya, their country of departure. This would constitute a breach of international law, under which migrants rescued in international waters cannot be returned to a place where their lives are put in danger. Both the United Nations and European Union have acknowledged that Libya is not safe.

Italy's coast guard said yesterday that the rescue had taken place in Libyan waters, not international waters, and was coordinated by the Libyan coast guard.

Proactiva spokeswoman Laura Lanuza said its members learnt the rescue occurred in international waters because their boat was nearby and they could listen to radio communications between the Italian ship and the Libyan authorities.

A spokesman for the U.N. migration agency said it could not establish the location of the rescue. He said the agency was still investigating the case but confirmed the return of the migrants to Libya.

The U.N. refugee agency said the operation "could represent a violation of international law," it said on Twitter.

Migrants' charities are at loggerheads with the new Italian government and its right wing home affairs minister Matteo Salvini who wants to reduce the number of migrants arriving on Italy's shores.

Since coming to power in a coalition government on June 1, Salvini has been making waves by turning away humanitarian ships that have picked up migrants from North Africa in the Mediterranean. Rome has also demanded that its European Union peers do much more to help Italy, which along with Greece has received the most migrants, pressing efforts to stop them coming at the source.

Salvini has come under fire from human rights groups and factions within the Roman Catholic Church for his uncompromising stance on migration, with a popular Christian magazine comparing him to Satan on its front cover last week. "So many enemies, so much honor," Salvini tweeted on Sunday, slightly tweaking a well-known saying of Italy's World War Two dictator Benito Mussolini on the 135th anniversary of his birth. At the same time, he dismissed concerns over racist attacks in Italy, saying migrants were to blame for a third of all crimes in the country.

His comments exacerbated anger on the left. "Violence is multiplying everywhere. But he denies it," said Maurizio Martina, head of the opposition Democratic Party (PD).

At least eight migrants from various African countries have been shot by air rifles since the start of June in possible racist attacks. In addition, a Roma baby was hit by an air pellet and risks being paralyzed for life. The Italian who fired the gun has denied aiming at the child. The U.N. migration agency (OIM) said there had been 11 racist attacks in Italy since mid-June. "[This represents] an extremely worrying trend of violence and racism," it said.