Egypt is holding up to 2,400 people who were arrested following attacks on two Sinai tourist resorts four months ago, according to a US human rights group.
Egyptian police officers guard the wreckage of the Taba Hilton hotel.
Human Rights Watch says the detainees have been held without access to lawyers or their families and that some have been tortured.
Egyptian officials say they are studying the HRW report.
Thirty-four people died in the bomb attacks, which targeted resorts popular with Israeli tourists.
105 people were also injured in three explosions at the Hilton hotel in Taba and a backpacker camping area near the resort of Nuweiba.
New York-based HRW group released its 48-page report into the alleged mass arrests on Tuesday.
"Egyptian security forces responded to the Taba atrocity by committing human rights abuses themselves," said Joe Stork of Human Rights Watch.
"If the government won't bring criminal charges against these detainees and give them fair trials, it must promptly release them," he said.
After a meeting with Interior Ministry officials, Mr Stork said they claimed to be holding only 200 people.
"I find that non-credible," said Mr Stork.
About 90 prisoners were released by the Interior Ministry on 4 February.
Challenged on the detentions last month, Egyptian President Hosni Mubarak said the reports were implausible because there were only a few thousand people in total in El Arish, the capital of North Sinai province at the centre of the arrest campaign.
Cabinet spokesman Magdy Rady has received a copy of the HRW report, but has not commented on it.
A Foreign Ministry statement on Tuesday said the government would study the report and "any proven violation will be dealt with according to Egyptian laws".
Despite the alleged mass arrests, the government has identified only nine people as being responsible for the attacks, HRW said.
The Interior Ministry named the alleged organiser of the attacks as a Palestinian man, Ayad Said Salah.
It says he died in the Taba blast along with another suspect.
A further suspect was shot dead by police following a gun battle in the Sinai earlier this month.
Police in October said they had arrested five men, all Sinai Bedouin, in connection with the attacks.
The government ruled out any link between the suspects and al-Qaeda.
One detainee who was later released told Human Rights Watch that Egyptian Security officers had bound his hands and suspended him from the top of an iron door, "causing excruciating pain to his shoulders."
The officers then gave him electric shocks through wires attached to his toes, according to the account.
In a statement, the group urged the Egyptian government to carry out a thorough and impartial inquiry into allegations of torture and arbitrary arrest and prosecute any officials found to have violated the law.