Ankara wants to try Metin Kaplan, the leader of an Islamist group banned in Turkey who is based in Cologne, for plotting in 1998 to crash an aircraft into the mausoleum of Kamal Ataturk, founder of the modern Turkish state.
"We will not allow any maltreatment (of Kaplan)," Turkish Interior Minister Abd Al-kadir Aksu said on Tuesday after talks with his German counterpart, Otto Schily.
Last month a German court rejected Turkey's extradition case because it feared Kaplan, who leads the Kalifatstaat group which wants to establish an Islamic state in Turkey, would not get a fair trial if he returned home.
Schily said Germany wanted to extradite Kaplan and that it had appealed against the court's decision, but added Turkey would have to provide more guarantees before an extradition could go ahead.
But Schily praised Turkey for approving political reforms over the past few years, aimed at improving its human rights record and winning a date for opening accession talks with the European Union (EU).
"Mr Aksu has expressed the determination of the Turkish government concerning the definite ending of torture, especially in police stations, and this carries great importance for us," he said.
Kaplan, known as "the Caliph of Cologne", served four years in a German jail for calling for the killing of a rival religious leader.
He was freed in May, but must report regularly to police.