Italian police have arrested four suspects in connection with the violent gang-rape of two underaged British girls at a birthday party in a small town in the country's south.

The incident allegedly happened Monday night at a house party in Marconia di Pisticci, a town of some 12,000 inhabitants in Italy's mountainous Basilicata region.

"The two victims were reportedly approached by two young men who seemed to have taken advantage of their physical state, possibly due to alcohol," said Pietro Argentino, public prosecutor in the nearby city of Matera.

"Two others arrived later and the rapes happened in a field next to the villa," Argentino told the AGI news agency.

The girls, one of who is said to have relatives in the town near the Gulf of Taranto, were allegedly slapped and punched before being gang-raped, local news reports said.

Both aged around 15, they told their parents what happened when they later arrived home and were taken by ambulance to a hospital in Matera.

Police arrested four men, all from Marconia di Pisticci and some of whom had criminal records. They are all between 19 and 23 years old.

Four other men are also being sought in the case.

"What happened is extremely serious, and we hope the judicial authority will do justice to the girls and their parents for what they had to endure," their lawyer Giuseppe Rago said.

"The girls are certainly not well," he told the AGI news agency.