Diplomats from several western countries are observing the trial of around 50 men at the state security court, and are "concerned" about reports the detainees have been badly treated in jail, one of them told AFP.

Ashraf al-Zannati, an Arabic language teacher at the British Council in Cairo, said through the bars of the courtroom cage that he and other defendants were subjected to a weekly "session of torture".

"We had one two days ago. You have to take off your t-shirt or whatever you're wearing and they get other people to hit you on the back," he told AFP, after being bustled into the state security court by guards.

"They use wire and they usually hit us on the back so it doesn't show, and with their hands," said Zannati, adding that guards also threw their food onto the ground, making it inedible.

Other defendants hid from reporters by covering their faces with handkerchiefs.

The group, branded "devil worshippers" by the local press, was reportedly arrested following a May 11 party on the Queen Boat nightclub on the Nile in central Cairo, but several defendants were arrested elsewhere.

The main defendant, Sherif Farahat, who also stands accused of "exploiting the Islamic religion to spread extremist ideas", told AFP his confession had been forced out of him.

While being interrogated, state security officers subjected him to "all that you can imagine", he claimed.

"I stayed there for more than three weeks, blindfolded. I could not see the people who were asking me questions and hitting me," he said.

Asked to give more details, Farahat said: "I'm afraid that they will hurt us if I tell you this, but electricity, this is the first thing I can tell you, not only to me but to other people."

Defendants had charged at previous court sessions that they were beaten and tortured, and the French section of rights watchdog Amnesty International has called for an investigation to be opened into the allegations of torture.

Defence lawyer Farid al-Dib also suggested in court that confessions had been forced out of the defendants and urged the presiding judge to clear them all, arguing that the state prosecution had fabricated the charges.

"The whole case, from beginning to end, has been oppression upon oppression," he told the court, after listening to the prosecution reading from defendants' confessions to having gay sex.

Dib accused the prosecution of "scandalising" the nation by "portraying Egypt as transformed into a land of gays", claiming none of the defendants were in fact homosexuals.

All the defendants are accused of "practising debauchery with men", although the practice of homosexuality is not explicitly prohibited under Egyptian law, based on Islamic law.

Those convicted could face up to five years in prison and state security court sentences cannot be appealed under decades-old emergency laws aimed at protecting public order.

Amnesty International complained in June that "the majority, if not all, of these men are detained purely on the grounds of their alleged sexual orientation".

Diplomats from Belgium, Britain, Canada, Denmark, France, Sweden, Switzerland and the United States have been following the trial due to the interest the case has drawn abroad.