The man, Ahmed Abu 'Ali, aged 23, a US national, is believed to be held in secret detention at al-Ha’ir prison in the Saudi Arabian capital, Riyadh. He has had no access to lawyers and his telephone calls to relatives in the USA ended abruptly in November.

Amnesty International has issued an Urgent Action appeal calling for Ahmed to be given access to lawyers, regular consular access and for him to be released immediately if he is not properly charged.

Amnesty International UK Director Kate Allen said:

"Reports that FBI officials tortured Ahmed Abu 'Ali are extremely alarming and we are calling on the US and Saudi authorities to act quickly to now guarantee his safety.

"Ahmed should be given full access to lawyers and consular officials and unless properly charged he should be immediately released.

"What is all the more alarming about this case is the fact that it comes after reports of detainees under American control being sent to countries in the Middle East for interrogation and torture.

"It is vital that Mr Abu 'Ali's well-being is guaranteed and that this whole affair is fully investigated."

Ahmed Abu 'Ali's sister Tasneem Ali said:

"We are in despair over his safety. We don’t know why he stopped calling us. The US Embassy in Saudi Arabia is not telling us anything and won’t send a consul to check on him."

Ahmed Abu 'Ali was originally detained in Saudi Arabia in June 2003, having been arrested in Medina while taking an exam at al-Madina University. When initially arrested he was reportedly held in incommunicado detention for two months during which time he was allegedly tortured and ill-treated.

Since then, he has called his family in the US every two weeks but they last heard from him on 20 November 2004. The family has contacted the State Department in the US and the US embassy in Riyadh in order to determine Ahmed Abu 'Ali's fate. However they have reportedly not received any assistance.

On 16 December 2004, a US District Court Judge, in a lawsuit brought by Ahmed Abu 'Ali's family, stated that there was "considerable evidence" that the US were complicit in his capture. In addition, the US consul in Saudi Arabia did not visit Mr Abu 'Ali for almost a month after his arrest.

US federal agents were also allegedly involved in his interrogation and torture after his arrest. During an interrogation, FBI agents allegedly threatened him with either being declared an "enemy combatant" and sent to Guantanamo Bay, or with a trial in Saudi Arabia where he would have no legal assistance, public hearing or appeal to a higher tribunal.

According to his family, the Director of al-Ha’ir Prison informed the US embassy in Riyadh that Saudi Arabia was ready to hand Ahmed Abu 'Ali over at any time to the US authorities if a request was made to this effect.