Egypt has rejected a request by Italy for phone records relating to the death of Italian student Giulio Regeni in Cairo earlier this year.
A senior Egyptian prosecutor said handing over the records would violate his country’s constitution.
He told reporters that Italy had sought all phone records for areas where the student had stayed, where he went missing and where his body was found.
Rights groups have suggested security forces were to blame for the murder.
However Egypt says a criminal gang was behind his murder.
Egypt’s Deputy Prosecutor Mustafa Suleiman told a news conference in Cairo that the number of phone records requested by Italy could reach up to one million.
Handing these over, he said, would “violate the constitution” and “constitutes a crime”.
Mr Suleiman, who took a team of Egyptian officials to Italy this week, said his country would continue to co-operate with the Italian investigation into the killing of Regeni.
On Friday Italy recalled its ambassador Maurizio Massari for consultation over the case.
Many in Italy think he could have been targeted by the Egyptian intelligence services because of his research.
Giulio Regeni’s murder: What we know
The 28-year-old disappeared on 25 January. His mutilated body was found in a ditch on the outskirts of Cairo on 3 February.
Egypt’s initial autopsy report said Giulio Regeni had been hit on the head with a sharp instrument.
But evidence of torture came to light in a second autopsy by Italian doctors.
As a PhD student at the University of Cambridge, Mr Regeni researching trade unions and labour rights in Egypt, a sensitive topic in recent years.
Rumours about possible involvement of Egypt’s security services in the killing have been reported by the Italian press, activists and opposition groups.
Cairo investigators have suggested that Mr Regeni was kidnapped and killed by a criminal gang posing as members of Egyptian police.
Police then said they had killed all five members of the alleged gang in a raid and recovered some of Mr Regeni’s personal belongings.