Turkish authorities arrested Deniz Yucel - a reporter with Germany's Die Welt newspaper - last month on charges of propaganda in support of a terrorist organisation and inciting the public to violence.
Germany has rejected claims he was working as a spy as tensions rose in diplomatic relations between the two countries.
Speaking to an Islamic Foundation meeting in Istanbul, Turkish President Recep Tayyip Erdogan has done little to soothe those tensions, criticising German chancellor Angela Merkel.
"And then she asks for a terrorist agent, supposedly a journalist, who was hiding in a German consulate for a month. She asked us to return him. I told her we have justice. He should be put on trial. We won't send him before his trial."
The President says Ms Merkel shouldn't be advocating his return.
"Does this comply with political ethics? Does this comply with the understanding of justice? Your duty, as a politician, is not to support backers of terrorists but hand them over."
President Erdogan accuses Germany of implementing what he calls Nazi measures.
"Against who? Against my Turkish brothers who live in Germany, against my ministers and lawmakers who go there."
Germany banned some Turkish ministers from speaking to rallies of expatriate Turks ahead of a referendum next month, citing public safety concerns.
The Turkish President's bid to boost his powers in the April 16 referendum has sparked protest in Germany, with more than 1.4 million Turkish residents in Germany eligible to vote.
This demonstrator says she is determined to raise her voice against him.
"We don't need any Erdogan, we don't need him. His people are going to say 'yes' and we need a 'no, no, no!'. I am against Erdogan. That's it. He is a dictator."
Deniz Yucel was initially detained after he reported on emails that a leftist hacker collective had purportedly obtained from the private account of Turkey's energy minister, who is also President Erdogan's son-in-law.
