A new report by a leading human rights group says the United States and other countries have secretly sent dozens of Islamist detainees to Egypt, where they have most likely been tortured, in the past decade.
The 53-page report by Human Rights Watch said Egypt is the world's main recipient of detainees.
The report, titled Black Hole: The Fate of Islamists Rendered to Egypt, identifies 61 people who have been transferred into Egyptian custody since 1994.
However some experts quoted by the report say the actual number of people sent to Egypt is much higher, as such transfers usually occur in secret and without legal safeguards.
The report cites analysts, lawyers and Islamic activists who believe 150 to 200 detainees have been transferred since the September 11, 2001, attacks on the US.
Those transferred to Egypt, most of them Egyptians suspected of Islamist militancy, include people believed to offer useful intelligence for US authorities in Washington's war on terrorism.
Others mentioned in the report were two Yemenis transferred to Egypt, one to Yemen and another to US custody at Guantanamo Bay in Cuba.
"Egypt ... has been the country to which the greatest numbers of rendered suspects have been sent," said the report.
While most of the countries transferring detainees to Egypt are Arab or South Asian, Sweden and the US are also on the list.
"The person sent back to Egypt under these circumstances is almost surely going to be tortured," Human Rights Watch deputy Middle East director Joe Stork said.
He said torture and other forms of mistreatment are so prevalent in Egypt that by sending detainees there, countries are violating the international convention against torture.
The report calls on foreign governments to halt the practice, at least until Egypt can prove it does not mistreat prisoners.
"Do not under any circumstances extradite, render, or otherwise transfer to Egypt persons suspected or accused of security offences unless and until the government of Egypt has demonstrated that it has ended practices of torture and ill-treatment," the report urged.
The report cited the case of Egypt-born Australian Mamdouh Habib, who said he was detained in Pakistan in the weeks after the 9/11 attacks and was interrogated by US agents before being sent to Egypt.
He has repeatedly alleged he was tortured in prison there for six months before his transfer to Guantanamo Bay.
Mr Habib was released and returned home earlier this year.
The ABC reports that the Egyptian Supreme Council for Human Rights has backed torture allegations by Egyptian police and security forces, in its first annual report.
US President George W Bush earlier this year insisted Washington does not engage in torture or send suspects to countries without assurances they won't be mistreated.
"We operate within the law and we send people to countries where they say they're not going to torture the people," he said at an April 28 news conference.
US officials said a classified directive signed by MR Bush after 9/11 gave the CIA broad power to transfer detainees without approval from the White House, according to Reuters.