Criticism and protests followed the decision to cancel a controversial "Palestine Congress" in Berlin on Saturday, which was originally set to run for three days but was halted hours after it opened.
The organizers of the conference said that the police had undermined democratic rights by cancelling the event.
Police on Friday broke up the pro-Palestinian conference in the Tempelhof area of Berlin and asked some 250 participants to leave the hall just two hours after the event began.
Organizers of the conference had decried Israel's ongoing military offensive in the Gaza Strip, and attacked the German government's support for the Israeli government.
Lawyer Nadija Samour said on Saturday on behalf of the organizers that the actions by the police were completely disproportionate and that less extreme measures would have been possible. She said the police torpedoed all attempts to protect the assembly.
No criminal statements were made, she said, a fact the police had also admitted.
The authorities said on Friday that the conference was halted due to a video broadcast of a speech by a man who is banned from political activity in Germany for hate speech against Israel and Jews.
When the man spoke, several police officers intervened, cut the transmission and temporarily switched off the power.
The authorities saw a danger "that such anti-Semitic, violence-glorifying and Holocaust-denying speeches could be repeated at the event," a police spokeswoman said.
The ban was not known to the organizers and had only been communicated shortly beforehand, Samour said. From the organizers' point of view, the police measure was unlawful and an objection was lodged with the police to be able to continue the assembly, she said.
Nearly 2,000 people demonstrated against the cancelled event in rallies registered by the conference organizers. Up to 1,900 people came, according to police, who said the protest was largely peaceful. There were shouts of "Viva, viva Palestine," "Palestine will never die" and "Israel bombs - Germany finances" at the gathering.
Nearby, a small group of demonstrators turned out carrying Israeli flags.
Some 900 officers were deployed throughout the city, mainly at the demonstration, with additional officers brought in from the states of North Rhine Westphalia, Hamburg and Mecklenburg-Vorpommern.
The organizers had registered a demonstration of 1,500 people for Saturday against the ban on the event, a police spokesman said.
The protests came after a calm night in the capital despite the imposition of the ban on the event that was originally due to run for three days.
Security sources said several leading activists wanting to attend the congress were banned from entering the country in steps that were coordination with the federal and state security authorities in Berlin.
Interior Minister Nancy Faeser earlier praised the police's efforts on X, formerly Twitter.
"It is right and necessary for the Berlin police to crack down on the so-called Palestine Congress. We do not tolerate Islamist propaganda and hatred against Jews," Faeser wrote.
The police union also called the crackdown by officers a "strong signal in the direction of those who exploit [German] democracy or doubt the assertiveness of the capital's police force."
"Anyone who wants to utilize our democratic opportunities must also comply with regulations and laws," regional police union head Stephan Weh said in a press release.