The body of an Italian student who disappeared last week in Cairo has been found and shows clear signs of torture, a senior Egyptian prosecutor has said.
Giulio Regeni, 28, disappeared on the evening of 25 January, after leaving his home to meet a friend.
His body was found beside a road in Cairo's western outskirts on Wednesday.
Senior prosecutor Ahmad Nagi said the cause of death had yet to be determined but Mr Regeni's body had bruises, knife wounds and cigarette burns.
He said the injuries covered "all of his body, including his face". Mr Regeni was found naked from the waist down and appeared to have suffered a "slow death", Mr Nagi added.
Earlier, another Egyptian official had suggested that Mr Regeni, a PhD student at Cambridge University in Cairo to conduct research, may have died in a road accident.
The Italian foreign ministry in Rome summoned the Egyptian ambassador to express its concern on Thursday morning.
A statement said the ministry expected "maximum collaboration", adding that the ambassador "assured us Egypt will co-operate fully in finding those responsible".
Mr Regeni, a PhD student at the department of politics and international studies at the University of Cambridge, was a visiting scholar at the American University in Cairo (AUC).
He is reported to have been carrying out research on trade unions and labour rights in Egypt - a sensitive topic in recent years.
"It has become increasingly difficult and dangerous to conduct research," said Amy Austin Holmes, head of the sociology department at the AUC. She said she knew of researchers who had been denied entry to Egypt or arrested.
Friends said Mr Regeni left his flat at 20:00 local time on 25 January, planning to take the metro to central Cairo to meet a friend.
Italians exasperated - Julian Miglierini, BBC News, Rome
"Bewilderment" is the word used by the Italian foreign ministry to sum up its furious reaction to the conflicting versions of the circumstances of Giulio Regeni's death.
Initial reports from Egypt said his body showed signs of torture. These were then contradicted by claims that the 28-year-old might have been the victim of a traffic accident. But a prosecutor now says Mr Regeni suffered stab wounds and cigarette burns, pointing to a "slow death".
These contradictions are making headlines in the Italian media and were enough for the government to issue a harsh statement which said it had summoned the Egyptian ambassador - and urged Cairo to "immediately" launch a joint investigation to ascertain what happened to Mr Regeni.
There was a heavy police presence in the capital that day because it was the fifth anniversary of the start of the uprising against former President Hosni Mubarak.
Several activists were arrested, while others went into hiding.
The area where Mr Regeni was going to meet his friend was near Tahrir Square, the symbolic centre of the 2011 uprising.
Cambridge University said: "We are deeply saddened to hear news of the death of Giulio Regeni. Our thoughts are with his family and friends.
"The vice-chancellor and the Mistress of Girton College [where Mr Regeni was studying] have been in contact with Giulio's family."