Several right-wing activists occupied Berlin's landmark Brandenburg Gate on Saturday, according to police.
About 15 members of the Identity Movement climbed on top of the monument and hung a banner reading "Secure borders - secure future" from the gate's horse-drawn chariot statue, before climbing down about an hour later after police demands.
The right-wing group is radically opposed to foreign and Islamic influence in Germany, and has been active since 2012.
It is currently being monitored by the German intelligence service for alleged efforts to undermine civil liberties.
Berlin Mayor Michael Mueller and the city's Interior Minister Frank Henkel strongly condemned the protest.
"It is simply disgusting that with this kind of action the enemies of democracy are trying to appropriate a symbol that stands for a democratic, free and open German," Mueller said.
The group said on its Facebook page that it wanted the protest to coincide with a government-organized awareness day on the topic of migration and integration.
Demonstrators quickly mounted a counter-protest on the square in front of the gate, chanting slogans against the Identity Movement.