Pro-Palestinian activists took down the German flag outside the Reichstag in Berlin on Sunday and raised a large Palestinian flag in its place, Berlin police said. Police detained three suspects. The action came a day before the 88th anniversary of Kristallnacht.

A 22-year-old man climbed the flagpole around 11:15am and raised the Palestinian flag, police spokesman Martin Halweg said. The pole is 28.5 metres high, and the German flag on it covers 60 square metres. The man said he acted out of "solidarity with Palestine".

He climbed down from the monument on his own around 12:30pm. Berlin's fire service said firefighters came to remove the Palestinian flag and took it down a few minutes later.

Police say the three detainees are Germans with no visible immigrant background. The 20-year-old suspect was later released.

Police have opened a criminal investigation over alleged "insulting the state and its symbols". They are also investigating trespassing. Halweg said police also see the action as a breach of the law on public assemblies.

The pro-Palestinian group "Peacefully Against Genocide" claimed responsibility. Last year, its activists climbed the Brandenburg Gate and unfurled a banner with pro-Palestinian messages.

The pole and flag outside the Reichstag, where the Bundestag, Germany's parliament, sits, form a national monument called the "Flag of Unity". It marks the reunification of Germany on 3 October 1990, after the fall of the Berlin Wall. Because of its symbolic status, the flag is not lowered to half-mast during national mourning, except in exceptional cases.

The Israeli embassy in Berlin said of the Palestinian flag: "Around the world, it is flown not as a symbol for Palestinians, but as a symbol of hatred towards Israel." The embassy said the flag stands against something rather than for something, and that in France it has been a flag of violent riots against the republic. The embassy said anyone who raises the Palestinian flag in Berlin and takes down the German one clearly shows they are against everything that black, red and gold stand for: freedom, democracy and the rule of law.

German politicians also commented on the case, among them Free Democratic Party leader Wolfgang Kubicki. He said those behind the action leave no doubt about their intentions. "They want to sow discord in our country and trample on the liberal-democratic values of our republic," Kubicki said.