Germany's domestic intelligence chief has warned of a radicalisation of right-wing groups amid a record influx of migrants and refugees, as xenophobic rallies and clashes shook several towns at the weekend.
Hans-Georg Maassen's comments come as Germany expects up to one million migrants and refugees this year.
Protests against refugee homes and clashes with police again rocked several towns at the weekend, mostly in the former communist East Germany.
"What we're seeing in connection with the refugee crisis is a mobilisation on the street of right-wing extremists, but also of some left-wing extremists" who oppose them, Maassen said on Deutschlandfunk public radio on Sunday.
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Police and soldiers guarded two buses carrying about 100 refugees on Saturday night to a shelter in the town of Niederau, in the eastern Saxony state, after right-wing protesters had rallied at the site, a former supermarket, since Friday.
More than 1,000 people also demonstrated against refugees in several towns in the eastern state of Mecklenburg-Western Pomerania on Friday, including in coastal Stralsund where three people were wounded in clashes with counter-protesters.
In the eastern city of Leipzig, the right-wing rally Offensive for Germany, organised by a local anti-Islam activist with about 400 marchers, sparked a larger left-wing counter-protest that police said drew more than 1,000 activists.
In the ensuing street clashes, the rival groups hurled rocks and fireworks at each other.
In the western city of Bremen, unknown persons attempted to set fire to a tent set to house refugees from October.
This year alone has seen 22 arson attacks against would-be or existing refugee shelters, said Maassen, whose service is called the Federal Office for the Protection of the Constitution.
Read more: Germany: Refugees are falsely claiming to be Syrian
On Friday, a spokesperson for Germany's interior ministry claimed that many asylum-seekers in Germany were falsely claiming to be Syrian.
"Thirty percent of those asylum-seekers who claim to be Syrian are not Syrians according to this estimate," Tobias Plate said.
In late August, German Chancellor Angela Merkel announced that Syrian refugees could stay in the country and apply for asylum rather than being deported.
The announcement marked Germany's suspension of the Dublin Regulation, which stipulates that refugees must stay in the country they first enter.