ROME (Reuters) - Italy threatened on Tuesday to impose "immediate and proportionate" measures against Egypt if Cairo did not cooperate fully in uncovering the truth behind the murder of an Italian student.

Giulio Regeni, 28, vanished from the streets of Cairo on Jan. 25. His body was discovered in a ditch on the outskirts of the Egyptian capital on Feb. 3, showing signs of extensive torture.

"If there is not a change in tack (by the Egyptian authorities), the government is ready to react, adopting measures that are both immediate and proportionate," Foreign Minister Paolo Gentiloni told parliament.

He did not elaborate, but the head of parliament's human rights committee said last month that Italy should recall its ambassador to Cairo and declare Egypt unsafe for visitors if the investigation went nowhere.

Egypt said Gentiloni's words were a hindrance rather than a help. "We refrain from commenting on these statements, which complicate the situation," the Foreign Ministry said in a statement.

Italian officials have openly ridiculed different versions of Regeni's death put forward by Egyptian investigators, including an initial suggestion that he had died in a traffic accident.

Gentiloni said a change of tack "means not accepting twisted and convenient truths. It means finding out who was responsible for having probably put Giulio Regeni under surveillance before he disappeared". He called for more cooperation with Italy.

Other parliamentarians then also took aim at Egypt.

"Too many lies have been administered to us, bit by bit, for us to believe them any more," said Pier Ferdinando Casini, a former head of the lower chamber.

After a series of delays, Egyptian investigators are due to hold talks with Italian magistrates in Rome on Thursday and Friday, Gentiloni said.

Human rights groups have said the torture marks indicate that Regeni, a postgraduate student at Britain's Cambridge University, was killed by Egyptian security forces, an allegation Cairo has repeatedly denied.

Story continues

Regeni's mother said last week that her son's body had been so disfigured that she had only been able to recognize him by the tip of his nose. She has threatened to release the photographs of his corpse if the killers are not found.

Italy has significant economic interests in Egypt, including the giant offshore Zohr gas field, being developed by Italy's state energy producer Eni.

(Reporting by Philip Pullella; and Crispian Balmer; Editing by Kevin Liffey)