BERLIN (AP) — Germany's foreign minister expressed cautious optimism Wednesday that Berlin and Ankara may begin to slowly reel diplomatic relations back to normal, following an escalation of tensions that culminated with Turkish President Recep Tayyip Erdogan accusing Germany of "Nazi practices."

Foreign Minister Sigmar Gabriel said talks at a Berlin hotel over breakfast with Turkish Foreign Minister Mevlut Cavusoglu, the first face-to-face official meeting since the diplomatic crisis began last week, were "good, honest and friendly, but also hard and contentious."

Over the past week, German municipalities have canceled several events in which Turkish Cabinet ministers had planned to address rallies in Germany in support of a national referendum on constitutional reform that would give Erdogan more powers. Officials have cited issues of overcrowding and fire safety, among other things.

Some rallies have gone ahead, most recently with Cavusoglu himself addressing a crowd in Hamburg late Tuesday night, though not at the venue initially planned.

Germany's federal government has expressed increasing irritation over Turkish officials using Germany as a campaign platform, though it emphasized that it wasn't involved in blocking the rallies and couldn't intercede with the municipalities that did so. About 1.4 million people of Turkish descent living in Germany are eligible to vote in the referendum.

Setting the stage for Wednesday's meeting, Cavusoglu repeated Erdogan's assertion late Tuesday, saying Germany's "practices are similar to those of the Nazi era."

"There are lines that should not be crossed, and one of those is the comparison with Nazi Germany," Gabriel said.

Cavusoglu toned down his rhetoric after Wednesday's meeting, saying only that it seemed Germany was allowing anti-Erdogan campaigners to express their opinions while preventing his supporters from doing so.

"This does not fit democracy," he said at a Berlin trade fair. "Germany should not take sides."

Adding to bilateral tensions, Turkey arrested German newspaper reporter Deniz Yucel, whom Erdogan has accused of being both a German spy and a "representative" of the outlawed Kurdish rebel group PKK — a claim Germany has dismissed as "absurd" — and has not yet allowed any German consular access to him.

Yucel, a reporter for Die Welt, was detained in Istanbul on Feb. 14 over his reports about a hacker attack on the email account of the country's energy minister.

Gabriel said he pushed for access to Yucel, who has both Turkish and German citizenship, and lobbied for his release.

Even before the current rift, relations were strained over Germany's criticism of Erdogan's crackdown following a failed coup as a flow of Turkish diplomats and soldiers sought asylum in Germany.

Germany has suggested it may not extradite suspects wanted by Turkey in cases it considers politically motivated, which has prompted Erdogan to accuse Germany of sheltering terrorists and having no regard for other countries' security issues.

The strife comes at a time when the European Union is relying on a migrant deal with Turkey that has significantly cut down the number of migrants crossing into Europe. Erdogan has several times threatened to quit the deal when expressing anger at the actions of European countries.

On Wednesday, a top German intelligence official said the domestic disputes in Turkey are affecting the security situation in Germany.

Hans-Georg Maassen, the head of Germany's BfV domestic intelligence service, said the splits seen in Turkish society are being mirrored among Turks in Germany.

"There is a danger that proxy conflicts between supporters of the (Kurdish) PKK and nationalist/far-right Turks will escalate," he said, citing the "high threat potential on both sides."

Erdogan himself said he hoped that what he described as "obstacles" being put in place by countries such as Germany would spur Turks to vote in the referendum.

"Those votes you cast will be the best response not just to all the countries in the West but to all the countries in the world," he told state-run TRT television. "God willing April 16 will be day that my citizens who have been hindered in the West and around the world will also celebrate."