German chancellor, Gerhard Schroeder, said on Tuesday the interior ministers of Germany and Turkey would meet to discuss the extradition of Metin Kaplan.
The leader of a banned Islamist group based in Cologne, Kaplan was accused of treason by Ankara.
But so far he had successfully resisted Turkish attempts to extradite him, arguing he would not face a fair trial if he returnsed home.
Turkey accuses Kaplan of planning a failed plot to crash an aircraft loaded with explosives into the mausoleum of Kemal
Ataturk, founder of the modern Turkish state, in 1998.
Ataturk oriented Turkey towards the West and cut the influence of Islam in politics and law.
A Cologne court last week turned down Turkey's attempt to extradite Kaplan, citing concerns a Turkish court might use information extracted from witnesses who had been tortured.
However, Schroeder said his government was appealing against the ruling, and said Germany and Turkey would discuss ways of ensuring concerns about a trial in Turkey were lifted.
"This verdict cannot be allowed to stand," he told a joint news conference with Turkish Prime Minister Tayyip Erdogan.
Gerhard Schroeder wants to
extradite Kaplan to Turkey
"We have agreed that the interior ministers are to meet to see if any additional guarantees are necessary and if they are, how they can be given," he said.
Kaplan, who wants to establish an Islamic state in Turkey, is the leader of a group known as the Kalifatstaat (Caliphate
State) that was banned in 2001 to stop what the German government called its "extremist activities".
Last week's ruling upheld an earlier decision to withdraw his right to asylum in Germany but let him stay in the country.
The trial has highlighted concerns over Turkey's human rights record as it presses to join the European Union.
But Erdogan rejected worries that Muslim Turkey is unsuitable for EU membership.
"We must show that there is no war between the cultures in Europe but a community of values," he said.