A far-right group opposed to immigration in Germany has hung a banner from Berlin’s Brandenburg Gate and distributed anti-Islamization flyers in one of the city’s major tourist hotspots.

Up to 15 members of the Identitarian Movement climbed the historic 18th-century gate on Saturday before unveiling a large banner which read “secure borders – secure future.”

The group, which is calling for an end to be put to the nation’s open border policy, also distributed leaflets demanding that the apparent “Islamization” of German society be thwarted, according to Reuters.

The movement, which has affiliate groups throughout the continent, suggested in Facebook post that Europe should become a “fortress,” explaining that their demonstration was intended to fight against “uncontrolled mass migration” to Germany.

“We send a signal to the Identitarian youth of Europe: Defend yourselves against the rampant immigration in your countries and against the Islamization moving more and more [sic],” the post added.

Saturday’s incident began at around 11 am and lasted approximately 50 minutes, during which time protesters set flares off from the top of the iconic city landmark.

Images on social media show the protesters using a large ladder to reach the top of the 26-meter sandstone structure, as shocked bystanders look on.

German far-right anti-immigration protesters climb Brandenburg Gate to protest immigration pic.twitter.com/NoX4E8qDh0 — ÇapaMagENG (@CapaMagENG) August 27, 2016

The far-right group is already under observation by German authorities because of its extreme stance against foreign nationals.

“Immigrants with Muslim background or people from the Middle East are being slandered by them in the most extreme fashion,” said Hans-Georg Maaße, head of the Federal Office for the Protection of the Constitution, earlier this month. “Therefore we are also surveilling this movement,” he added.

Berlin Mayor Michael Muller described the Brandenburg Gate protest as a “disgusting” act carried out by enemies of democracy, according to Germany’s RBB 24.

“Berliners will not allow the Brandenburg Gate [to be] misused as a symbol of exclusion,” he added.

Stemming from a right-wing youth movement in France, the pan-European ideology has gained traction in a number of countries opposing the movement of foreign nationals onto the continent.