By Amina Ismail

CAIRO (Reuters) - Egyptian security agents have abducted and tortured "at least several hundred people", some as young as 14, in an unprecedented spike in enforced disappearances aimed at silencing opponents, Amnesty International asserted in a report published on Wednesday.

The report, based on 70 interviews with former detainees, families of detainees, lawyers and others, said enforced disappearances had spiked since the appointment of Interior Minister Magdi Abdel Ghaffar in early 2015, with an average of three or four people reported disappeared every day.

"Enforced disappearance has become a key instrument of state policy in Egypt. Anyone who dares to speak out is at risk, with counter-terrorism being used as an excuse to abduct, interrogate and torture people who challenge the authorities," Philip Luther, director of Amnesty's Middle East and North Africa Programme, said in a statement that accompanied the report.

Amnesty said the nature of the enforced disappearances made it difficult to give a precise number, but that reports by Egyptian non-governmental organizations and rights groups indicated there had been "at least several hundred cases" since the beginning of 2015.

It counted cases where individuals were arrested by state agents and held for at least 48 hours without referral to the prosecution and where authorities denied they were in custody when asked by families.

The foreign ministry said in a statement that Amnesty reports on Egypt were biased, politically-motivated and aimed to harm its image. It declined to comment on specific accusations.

An interior ministry official who declined to be named said there was "no such thing as enforced disappearances" in Egypt. He said the ministry had looked into all suspected cases and in each instance had proven that the individual in question was remanded in custody on the orders of a prosecutor.

The report features the detailed cases of 17 people subjected to enforced disappearance, held incommunicado for periods ranging from several days to seven months without access to their lawyers or families.

Amnesty said many of those forcibly disappeared were held at Lazoughly, a compound run by Egypt's Homeland Security.

There, detainees are subjected to electric shocks, violence and sexual abuse to extract confessions, the report said, citing testimonies from at least seven named victims or their families.

Amnesty said it found similarities between wounds sustained by Guilio Regeni, an Italian student who disappeared in Cairo on Jan. 25 and whose body was found nine days later showing signs of extensive torture, and those that result from the methods of torture it said Egyptian security forces use when interrogating suspects.

Egyptian intelligence officials and police sources have told Reuters that on the day Regeni vanished, he was detained by police and then transferred to a compound run by Homeland Security. The police and Interior Ministry deny they were involved and say they never held Regeni.

The Interior Ministry has also said cases of police abuse were isolated and promised to investigate any allegations.

The report also accused Egypt's public prosecution of failing to properly investigate torture allegations and charging defendants based on confessions extracted under duress.

A judicial official who declined to be named as he was not authorized to speak to the media said prosecutors conducted random inspections of police compounds to ensure detainees were being held lawfully and this was not reflected in the report.

"All complaints received by the public prosecution are investigated," the official said.

(Additional reporting by Lin Noueihed, Haitham Ahmed and Ahmed Mohammed Hassan; Editing by Lin Noueihed, Michael Georgy and Robin Pomeroy)