Tens of thousands of supporters of Turkish President Recep Tayyip Erdogan are planning to rally in the German city of Cologne on Sunday, as tensions over Turkey's failed coup put authorities on edge.
Since the attempted military power grab on July 15, Erdogan's government has launched a crackdown on those allegedly linked to the putsch that has seen the detention of almost 19,000 people, sparking international concern.
Erdogan on Saturday signalled plans to tighten his grip through constitutional changes which would bring the Turkish spy agency and the military chief of staff directly under his control.
The political strife in Turkey has also found expression in Germany, which is home to the biggest Turkish diaspora. Up to 30,000 people are expected to answer a call to take to the streets from around 1300 GMT issued by a pro-Erdogan group: The Union of European-Turkish Democrats (UETD), police said.
The North Rhine-Westphalia state, where Cologne is located, is home to about one third of Germany's three-million strong Turkish community. At the same time, several smaller counter-demonstrations are to take place, including one billed "Stop Erdogan", and another called by far-right activists, raising fears the demonstrators could clash.
Security services in Germany sought to head-off any potential violence between the different camps, with some 2,700 officers, including several Turkish speakers, deployed to keep the peace.
Cologne's police chief Juergen Mathies warned: "One thing I want to make clear is that we will intervene against any kind of violence quickly, decisively and forcefully."
Amid fears that the crowd could be further riled by live screenings of speeches made from Turkey by politicians including Erdogan, Germany's constitutional court banned an application for such broadcasts.
Nevertheless, Turkey's sports minister will attend, said Mathies, adding that he had been able to stop the foreign minister from participating.
The tension comes at a time when relations between Germany and Turkey are already strained over the German parliament's recent decision to brand as genocide the World War I-era Armenian massacre by Ottoman forces. German politicians, led by Chancellor Angela Merkel, have issued strongly worded statements against Erdogan's crackdown following the putsch.
The hardline response "flouts the rule of law", Merkel's spokesman Steffen Seibert has said, also blasting "revolting scenes of caprice and revenge" in the wake of the failed coup.
At the same time, Ankara is demanding that Germany extradite suspects linked to US-based preacher Fethullah Gulen, whom Erdogan accuses of masterminding the power snatch.
The 75-year-old has strongly denied any involvement. Erdogan enjoys a large support base among the diaspora in Germany, home to some 1.5 million people with Turkish nationality who can vote in Turkish elections.
His AKP party garnered 60 per cent in the country in last November's election, a bigger share of the vote than in Turkey. Germany's integration commissioner Aydan Ozoguz underlined Erdogan's influence, saying he was concerned that "the relationships of people living here with Turkey are being massively exploited politically."
In the days following the botched coup, pro-Erdogan activists have stormed locations in Germany popular with Gulen's followers. Critics of the Turkish president have also complained of abuse and threats against them on social media.
German Foreign Minister Frank-Walter Steinmeier on Saturday warned in an interview with Sueddeutsche Zeitung daily: "It is not right to bring Turkey's domestic political tensions here... and intimidate people who have other political convictions."