The suspects are all members of the National Security Agency, including a colonel who previously met Italian prosecutors as part of murder probe
Italian prosecutors have placed five members of Egypt's security forces under official investigation for their alleged involvement in the disappearance of student Giulio Regeni, a judicial source said.
Regeni, a 28-year-old postgraduate student at Cambridge University, vanished in Cairo in January 2016. His body was found almost a week later and a post-mortem examination showed he had been tortured before his death.
There was no immediate comment from authorities in Egypt. Egyptian officials have repeatedly denied any involvement in Regeni's killing.
The five suspects are all members of the National Security Agency and include a general, two colonels and a major, the source said.
One of the colonels met Italian prosecutors during their first visit to Cairo in February 2016 after Regeni's disappearance. He had assured them that local security forces had had nothing to do with the disappearance.
All suspects have been placed under investigation for allegedly kidnapping Regeni. No one has yet been named in connection with the killing itself.
Intelligence and security sources told Reuters that police had arrested Regeni, who disappeared on 25 January 2016, outside a Cairo metro station and then transferred him to a compound run by Homeland Security.
Italian and Egyptian investigators have been working together to try to solve the crime and have held regular meetings in Rome and Cairo to pool their information.
But judicial sources in Rome told Reuters last week that Italy was frustrated by the slow pace of developments in Egypt and had decided to press ahead with its own line of inquiry in an effort to move things forward.
In a largely symbolic move, the Italian parliament suspended all ties with its Egyptian counterpart last week as well, and Foreign Minister Enzo Moavero summoned Egypt's ambassador.
Egypt's state information service said on Monday that Italy had sought Egypt's approval for listing "a number of Egyptian policemen" as suspects during a meeting of the prosecutors from the two countries last week.
It said such a request had already been rejected in the past because Egyptian law does not recognise the procedure for placing suspects under investigation before possible charges are laid.
It also cited a lack of solid evidence for the request, which, it said, was "merely based upon initial police inquiries".
Regeni had been researching Egypt’s independent unions for his doctoral thesis. Associates say he was also interested in alternatives to the long-standing domination of Egypt’s economy by the state and the military.
Both subjects are sensitive in Egypt. The military’s grip on the economy is a subject rarely talked about in a country that has been ruled almost entirely by military men since the overthrow of King Farouk in 1952.