The trial of four Egyptian intelligence officers accused of torturing the Italian student to death in 2016 has been stymied by Cairo's refusal to hand over their legal abodes in order for them to be informed they are on trial.

The four are National Security General Tariq Sabir and his subordinates, Colonels Athar Kamel Mohamed Ibrahim and Uhsam Helmi, and Major Magdi Ibrahim Abdelal Sharif.

They have been accused of abducting the Cambridge doctoral researcher on January 25, 2016 and dumping his remains in a ditch outside Cairo on February 3.

The body that was so badly mutilated his mother only recognised him by the tip of his nose.  

The Egyptian intelligence service reportedly suspected Regeni, 28, from the Friuli region, was a spy because of his research activity for the British university on the politically sensitive issue of Cairo street seller unions.

Egyptian President Abdel Fattah el-Sisi has repeatedly promised to collaborate with Italian prosecutors but there has been no substantive follow-up to his words.

"We are here to give a sign of solidarity with Giulio Regeni's family and the many people who over the years have never stopped asking for truth and justice," said Schlein after embracing Regeni's parents, Claudio Regeni and Paola Deffendi.

The Regenis on Sunday urged the four Egyptian spies "not to be cowards" and to turn up for the Rome hearing.

"We strongly believe that this trial must go ahead, it must be carried out, and we are here with this hope," Schlein added.

Rome prosecutors said the Constitutional Court should step in and try to break the impasse in the trial caused by Egypt.

The Rome Public Prosecutor's Office said it was asking the Rome preliminary hearings judge (GUP) in charge of the case to refer it to the Constitutional Court in order to overcome the "stasis".

The move was urged by prosecutor Francesco Lo Voi and deputy prosecutor Sergio Colaiocco in court on Monday.

The request concerns the issue of the constitutionality of an article in the Code of Criminal Procedure on the subject of the "absence" of the accused.

The judge reserved his decision, adjourning the proceedings to 31 May.

ANSA