BERLIN (Reuters) - German police arrested six members of the far right who were handing out tear gas bottles and flyers in the eastern city of Cottbus on Thursday and said they were stepping up security ahead of an anti-refugee protest there on Saturday.

Cottbus, a city of 100,000 residents in the state of Brandenburg, is home to 3,400 refugees. Tensions there have risen since five Syrian teenagers were detained in January over two knife attacks.

The six men arrested belonged to the far-right National Democratic Party (NDP), police said.

“An investigation has been launched against the men aged 17 to 32 years on suspicion of breaching the law on public assembly and their flyers and CS-gas sprays have been confiscated,” the Cottbus police said in a statement.

The NPD, which Germany’s Constitutional Court last year said resembled Adolf Hitler’s Nazi party, and other far-right groups have been organizing demonstrations demanding that refugees leave Cottbus.

The police told Reuters it planned to step up security in the city on Saturday, when far right groups plan another protest and refugees have planned a counter demonstration with their supporters, including activists from the far-left Linke party.

Last month, two Syrian teenagers injured a 16-year-old German boy with a knife and a group of three Syrians aged under 17 threatened a German couple with a knife outside a mall in Cottbus.

The anti-immigrant Alternative for Germany (AfD) came first in Cottbus in an election last year, beating Chancellor Angela Merkel’s conservatives amid public concern over Merkel’s decision in 2015 to welcome more than a million asylum seekers.

Anxiety about immigration is high in Cottbus like in many eastern regions in Germany where older generations grew up under communism, having little contact with foreigners.

Its technical university draws hundreds of international students each year, and the influx of foreigners and refugees has stopped the population from shrinking below 100,000 from about 145,000 on the eve of German reunification in 1990.

The Constitutional Court last year ruled against banning the NPD, saying it was too weak to endanger democracy.