Thousands of police officers were bracing for a demonstration by an estimated 30,000 supporters of Turkish President Recep Tayyip Erdogan in the western German city of Cologne on Sunday.
The first participants had already arrived for the event that was officially due to kick off at 3 pm (1300 GMT).
The demonstration, organized by European-Turkish organization UETD under the motto "Yes to democracy. No to the coup," was called to protest the coup attempt on July 15 in Turkey that left more than 260 people dead and triggered mass arrests and purges of the military, government and civil service.
Representatives of all Turkish political parties, including the opposition, are scheduled to speak, UETD general secretary Buelent Bilgi told dpa, noting that no members of the Turkish government were expected to attend.
Authorities had considered a ban on the protest in the event that high-ranking members of the Turkish government attended and increased security risks.
Rally organizers wanted to carry a live-stream video feed at the event of Erdogan speaking from Turkey, but the head of police issued a ban on such a broadcast.
About 3 million people of Turkish heritage live in Germany, and the failed coup has sown deep divisions within the community.
Tensions between Germany and Turkey have intensified since the coup, which Ankara blames on US-based cleric Fethullah Gulen, who has an estimated 100,000 followers in Germany.
The city was on edge for the possibility of violence, with police saying 2,700 officers would be deployed for the event.
"I have received countless letters, emails and calls from concerned citizens," Cologne Mayor Henriette Reker said.
Four counter-demonstrations attracting up to 1,500 protesters each are also scheduled in the city Sunday.
One is supported by the German far-right political party Pro NRW. Another counter-demonstration, organized by the alliance Cologne against the Right, is directed both against the Erdogan supporters and against Pro NRW.
A third protest event is planned by the youth organisations of the Social Democrats, the Liberals, left-wing party Die Linke and the Greens.
The fourth counter-demonstration will be held in the Deutz district near the pro-Erdogan rally by the left-wing group International Krefelders to protest "Erdogan's influence in Germany."
Cologne's police chief Juergen Mathies had acknowledged earlier in the week that "extremely different political opinions" would come together on Sunday and warned that his force would counter "any form of violence."