ROME (AFP) - Egyptian investigators began briefing Italian counterparts on Thursday (April 7) on a much-criticised probe into the slaying of an Italian student in Cairo that threatens to poison relations between the two countries.

The delegation of prosecutors and police arrived in Rome with a 2,000-page file on an investigation in which more than 200 people have been questioned, according to Italian media reports.

The meeting aims at reassuring Italy that everything is being done to bring the killer of 28-year-old Giulio Regeni to justice.

Frustrated by the apparent lack of progress, Italian officials have warned of consequences if the Egyptians do not present a credible and detailed account of everything they know about the young man's gruesome fate. The talks are expected to continue into Friday.

The case is a testing one for Italian Prime Minister Matteo Renzi, who has fostered a close trade and security relationship with Egypt's military-backed President Abdel Fattah al-Sisi, but is under pressure to respond to public anger over the Regeni case.

"The relationship is a huge deal for Italy but Egypt has burnt most of its credit in the last two months in a not very smart way," said Mr Mattia Toalda, an expert on Italian foreign policy at the European Council on Foreign Relations (ECFR) in London.

The Cambridge student disappeared in central Cairo on Jan 25.

His body was found on the outskirts of the city on Feb 3 bearing the signs of torture which, an autopsy concluded, had been inflicted over several days.

His mother has said his body was so mutilated she could only recognise him by the tip of his nose and global media coverage of the case has focused international attention on other disappearances and rights abuses in Mr Sisi's Egypt.

Italian officials were initially told that Mr Regeni had been killed in a car accident, then that his death had been linked to a personal dispute.

At the end of last month, Egypt publicly announced police had killed four members of a criminal gang specialising in abducting foreigners, and that they had found Mr Regeni's passport in the apartment of a sister of one of the slain suspects.

That version of events was greeted with outraged scepticism in Italy, where there is a widespread suspicion that the murder was the work of elements in the security services - a theory Cairo dismisses as without foundation.

Foreign Minister Paolo Gentiloni told Parliament on Tuesday the kidnapping gang story was a "new attempt to give credence to a convenient truth", and that Italy was preparing "immediate and proportionate" action if the Egyptian delegation did not provide satisfactory answers.

Mr Toalda said he could not remember an Italian foreign minister speaking the way Mr Gentiloni did.

"Basically he is saying to Mr Sisi: 'You told us lies again and again, and now we have to do something'."

Italy's own investigators are still waiting to receive Mr Regeni's mobile phone records and CCTV images from the neighbourhood in which he was abducted.

Rome also wants to know if and why Mr Regeni was under surveillance prior to his abduction. The student had been researching labour movements in Egypt.

He disappeared on the fifth anniversary of the uprising that ousted longtime leader Hosni Mubarak, a day when Cairo was on a security lock-down and virtually deserted.

Mr Toalda said Italy's options in terms of action were limited to recalling its ambassador, warning its citizens against travel to Egypt on security grounds or seeking backing from its European Union partners to put pressure on Cairo over the case.

All are problematic. An ambassador callback risks being seen domestically as purely symbolic while a travel ban would hurt Egypt's battered tourism industry at the cost of escalating the rift with Sisi's government.

And other EU countries might not be keen to jeopardise their relations with Egypt to support Italy given Rome's past courting of the Sisi regime.

"A lot depends on whether the Egyptian team can come up with something that buys Mr Renzi more time in terms of public opinion, which is very inflamed over this issue," Mr Toalda said.

"If they don't it will be almost impossible for Renzi not to be seen to be doing something."