A Sudanese former prime minister appeared before prosecutors for questioning Thursday after he reportedly accused a counter-insurgency unit of rape and other abuses of civilians in Darfur. The National Intelligence and Security Service (NISS) filed a criminal complaint against Umma Party leader Sadiq al-Mahdi after he made the comments about the Rapid Support Forces (RSF). Mahdi arrived with several lawyers and about 100 supporters before spending close to 40 minutes with prosecutors, an AFP journalist said. Mahdi was questioned but has not been formally charged pending further investigation, one of his lawyers, Nabil Adieb, told AFP. The NISS, which has authority over the RSF, accuses Mahdi of distorting the image of the forces, threatening public peace, undermining the prestige of the state and inciting the international community against Sudan, newspapers reported. The NISS complaint against Mahdi comes as his party and others engage in a "national dialogue" with President Omar al-Bashir. A senior opposition politician has told AFP the process might lead to a new, coalition government and that Bashir is pushing for "a real change" because he realises the country is "collapsing". The security service is resisting the dialogue process, the politician said. At a news conference in Khartoum on Wednesday, commanders of the RSF denied their force had looted, raped or committed arson. "All the allegations against us are lies," an angry Mohammed Hamdan Dalgo, the unit`s field commander, shouted. Mahdi`s government was overthrown in the 1989 Islamist-backed coup which brought Bashir to power. The president and Defence Minister Abdelrahim Mohammed Hussein are wanted by the International Criminal Court for alleged war crimes in Darfur.