A United Nations observer at the trial of two of Muammar Gaddafi's sons in Libya has been detained on suspicion of "black magic". Ahmed Ghanem, one of a three-strong UN team monitoring the case, was detained by security units on suspicion of occult practices. Photographs of his identity card and possessions were posted on the internet after the detention on Sunday at Tripoli's maximum security al-Hadba prison, where the trial is being held. A source at the prison said Ghanem, an Egyptian, was detained upon arrival to monitor the case on Sunday after written material was found indicating possible "sorcery" or improper communications, and was later released by judicial police. It is unclear if such an offence is recognised under Libyan law. A UN spokesman confirmed the detention and said it was seeking an explanation from the Libyan authorities. The incident is the latest controversy to rock a trial condemned as "riddled with procedural flaws" by Human Rights Watch. Saif al-Islam Gaddafi, his younger brother Saadi and the former spy chief Abdullah al-Senussi are all charged with war crimes, but have complained of having neither lawyers nor access to evidence in a case that began last month. The decision by the international criminal court (ICC) to allow Libya to try Senussi, who is also wanted by The Hague, may be examined by the United Nations after complaints by his lawyers. Senussi's lawyers have written to the ICC saying Libya has denied them access to their client and have asked that the UN investigate the trial process.