BERLIN — Berlin police arrested a 53-year-old German man on suspicion of sending dozens of threatening letters to politicians, lawyers and journalists that were signed with the acronym of a neo-Nazi group, as officials warned Tuesday that statistics show a disturbing rise in far-right extremism across Germany.

Interior Minister Horst Seehofer said far-right crime rose 5.65% in 2020, accounting for more than half of all criminality categorized as "politically motivated." 

"This shows again that right-wing extremism is the biggest threat for our country," Seehofer told reporters Tuesday while announcing the annual statistics.

In carrying out Monday's arrest in Berlin, police seized an unencrypted hard drive with data that might help with an ongoing probe, said Holger Muench, the head of Germany's Federal Criminal Police Office.

"There was a lot of data, but it needs to be evaluated," he said.

The suspect, whose name wasn't released for privacy reasons, has previous convictions for "numerous crimes, including ones that were motivated by right-wing ideology," prosecutors in Frankfurt, who are handling the case, said.

The letters were signed "NSU 2.0." A German group called the National Socialist Underground was responsible for a string of violent crimes between 1998 and 2011, including the racially motivated killings of nine men with immigrant backgrounds and a policewoman. The group's name was derived from the full name of the Nazi, or National Socialist, party.

Police think the suspect sent almost 100 letters to dozens of people and organizations across Germany and Austria since 2018. German news agency dpa reported that investigators think the suspect may have obtained personal data on the people he targeted from official records or Darknet forums.

German security agencies warned of the growing threat of violent far-right extremism. In July 2019, a regional politician from Chancellor Angela Merkel's party was killed by a neo-Nazi; three months later, a gunman tried to force his way into a synagogue on Yom Kippur, killing two people.

Seehofer said the new statistics reveal an ongoing increase in anti-Semitic crimes in Germany, which was up 15.7% in 2020 over 2019 with 2,351 total incidents — 94.6% of which were committed by a far-right suspect. 

Of the total, 62 were acts of violence while the majority were anti-Semitic hate speech and other related crimes, frequently on the internet or over social media, Seehofer said. 

"This development in Germany is not only troubling, but in view of our history, deeply shameful," he said. 

In 2020, Germany recorded a 72.4% increase in anti-immigrant crimes, up to 5,298 total cases over 3,073 in 2019, Seehofer said. 

In the most deadly incident, nine people with immigrant backgrounds were shot dead in Hanau, near Frankfurt, in February by a gunman who had called for genocide.

Authorities have raised concerns about the role the Alternative for Germany party allegedly played in stoking a climate of resentment toward immigrants and the government. The party, which placed third in Germany's 2017 election, has moved steadily to the right in recent years, drawing increasing scrutiny from the country's domestic intelligence agency.

On Tuesday, Alternative for Germany's section in Berlin condemned a member who appeared to lament the absence of attacks on Chancellor Angela Merkel.

The news website Business Insider reported that AfD's former chairman in Berlin, Guenter Brinker, forwarded a message stating that "either that piece of dirt is so well protect that nobody can get at her, or don't the Germans have any balls?"

Brinker said later that he had mistakenly forwarded the message and regretted doing so, and that he rejected "all forms of hatred and violence."