BERLIN — Anti-Islam activists have staged an hour-long demonstration atop Berlin’s Brandenburg Gate.

The protesters unfurled a banner Saturday calling for “secure borders” in Germany as crowds of tourists milled around the iconic monument.

Police said 15 people were briefly detained over the protest and are likely to face charges of trespassing, harassment and breaching laws on public assembly.

Berlin police spokeswoman Patricia Braemer said the protesters belonged to the Identitarian Movement. Germany’s domestic intelligence agency said this month it was putting the far-right group under observation because it aims to subvert democracy.

Leaflets scattered by the group claimed the government is trying to replace Germany’s population with Muslim immigrants.

Germany has seen an unprecedented influx of asylum-seekers, many from Syria, Iraq and Afghanistan, over the past year.