The alleged assault took place in Florence on Wednesday night, when the two women claim two on-duty Carabinieri police officers raped them.
The women, aged 19 and 21, spent the evening at a nightclub where a group of police officers were called to break up a fight.
Four of the officers left shortly afterwards when calm was restored, and the remaining two offered the Americans a lift home; they were captured on CCTV footage getting into the police car.
Once they returned to the students' apartment in central Florence, the women claim the officers raped them.
Both women were examined in hospital on Thursday and investigators have confiscated the clothes they were wearing during the incident to carry out analyses, Florentine paper La Nazione reported.
According to police sources cited by Ansa, police then interviewed the women separately over the course of the day, "and found no inconsistencies in their stories".
Each year, the Tuscan city hosts thousands of US students at some forty universities and countless language schools.
Florence is the city with the country's second highest rate of reported sexual assaults, according to figures released by national statistics agency Istat earlier this year.
Istat data also showed that in the first six months of 2017, more than 2,000 people were charged with sexual assault in Italy - though the agency estimated that fewer than ten percent of the total number of sexual assault crimes are reported to police.