Germany is looking at protecting the Bundestag Parliament building after supporters of US President Donald Trump rampaged through the US Capitol, some in clothes glorifying Auschwitz.
German Foreign Minister Heiko Maas recalled the country’s Nazi history as he condemned the riots in Washington, DC.
Mr Maas also reminded people that Germany has had recent problems with far-right and anti-mask protests near the Bundestag in Berlin, and a terror attack in Halle.
In one of those protests, far-right activists came close to storming the Bundestag.
There has also been problems with far-right recruits in the military and police, and last year, Thomas Haldenwang, chief of the country’s domestic intelligence agency, said the far-right was its biggest threat.
“If people with ‘Auschwitz’ on their sweaters attack parliaments, our reaction must be very clear," Mr Haas tweeted.
"There should be no place for something like this anywhere, especially not in parliaments. Just hideous.
"The only answer to this can only be a clear and determined 'Never again'.
“It would be self-righteous to point a finger at America now. Here too, in Hanau, Halle, on the steps of the Reichstag, we had to experience how agitation and inflammatory words turn into hateful deeds.”
Halle is a reference to the unrepentant neo-Nazi gunman, Stephan Balliet, who was jailed in December for a terrorist attack on a synagogue after admitting he was motivated by anti-Semitism.
The president of Germany's lower legislative house, Wolfgang Schauble, said he would examine "what conclusions should be drawn from this for the protection of the Bundestag”.
German Chancellor Angela Merkel has asked the embassy in Washington to provide a report on the "violent excesses in the Capitol".
Mrs Merkel expressed shock at the disturbing, violent protests.
"We all saw the unsettling pictures of the storming of the US Congress, and these images made me angry and also sad," she said.
"A ground rule of democracy is that after elections there are winners and losers. Both have their role to play with decency and responsibility so that democracy itself remains the winner."
Mr Maas was the first German politician to react to the US riots.
"The enemies of democracy will rejoice at these inconceivable images from Washington DC," he tweeted.
"Seditious words turn to violent actions – on the steps of the Reichstag and now in the Capitol. Contempt for democratic institutions has devastating effects."
"Trump and his supporters should finally accept the decision of the American voters and stop trampling democracy underfoot."
Balliet streamed the shooting on Yom Kippur, the holiest day of the Jewish year, in Halle in eastern Germany in 2019.
Presiding judge Ursula Mertens described the attack, in which two people were killed, as cowardly when she announced the verdict on Monday.
An elite unit in Germany’s Special Commando Forces was formally disbanded this year after some of its members were found to hold extreme far-right views.