Two US teenagers are in police custody in Rome after a 35-year-old Italian policeman was fatally stabbed following a drug deal gone wrong.
Two US teenagers have been jailed in Rome as authorities carry out a murder investigation into the killing of an Italian police officer.
A detention order issued by prosecutors named the pair as Gabriel Christian Natale Hjorth and Finnegan Lee Elder, according to Italian state broadcaster RAI.
The detention order said they were both born in San Francisco in 2000. Police said they were 19.
Prosecutors said in the order that Elder is the main suspect, accused of repeatedly stabbing Carabinieri paramilitary policeman Mario Cerciello Rega, 35.
Rega was investigating the theft of a bag after a drug deal gone wrong in Rome.
Natale Hjorth is accused of using his bare hands to strike the officer's partner, who wasn't seriously injured in the attack.
Both teenagers were also being investigated for attempted extortion.
Elder's lawyer Francesco Codini said his client exercised his right not to respond to questions during a detention hearing held on Saturday in the Rome jail where the two teens are being kept.
Natale Hjorth's lawyer wasn't immediately available for comment.
An Italian investigator who wished to remain anonymous said the pair had snatched the bag of a drug dealer in Rome after the man apparently gave them "a different substance" instead of cocaine.
The Carabinieri said the Americans demanded a 100 euro ($A161) ransom and a gram of cocaine to return the bag.
The alleged dealer called the police, saying he had arranged a meeting with the thieves to get his bag and phone back.
Police said there was a scuffle at the rendezvous site and the policeman was stabbed eight times, dying shortly afterwards in the hospital.