Germany’s top security official offered to send federal assistance to the eastern state of Saxony on Tuesday following violence during a far-right protest in the city of Chemnitz that left at least 18 people injured.

The protest late Monday, sparked by the killing of a 35-year-old German man in an altercation with migrants over the weekend, erupted into clashes between neo-Nazis and left-wing counter-protesters. Opposition parties criticized police for failing to prevent the violence.

“The police in Saxony are in a difficult situation,” Interior Minister Horst Seehofer said. “Should it be requested, the federal government will provide police support.”

He was backed by Chancellor Angela Merkel, who condemned the violence.

“Should Saxony need help to maintain law and order, and to uphold the law, the federal government stands ready,” she said.

Saxony’s police chief Juergen Georgie acknowledged authorities had underestimated the size of the protest. Initial estimates had forecasts about 1,000 far-right protesters and half that number of counter-protesters would descend on Chemnitz, he said.

In the end, some 600 officers struggled to prevent 6,000 supporters of the far-right from breaking through police lines. Footage showed demonstrators performing Nazi salutes and chanting “the national resistance is marching here!”

Georgie said the police presence in Chemnitz would be stepped up in the coming days, with more protests planned.

Green lawmaker Konstantin von Notz urged Seehofer to consider resigning, accusing him of fanning anti-migrant sentiment over the past year. Von Notz told the news portal t-online.de that the violence in Chemnitz recalled events elsewhere in eastern Germany during the early 1990s, when authorities failed to stop far-right mobs from attacking migrants.

The state of Saxony has long been a hotbed of anti-migrant sentiment, with some accusing police of turning a blind eye to sympathizersin their own ranks. The far-right Alternative for Germany party received almost a quarter of the vote in Chemnitz last year.

Chemnitz police said they have arrested a 22-year-old Syrian and a 21-year-old Iraqi on suspicion of manslaughter in the stabbing death of the German man after a street festival early Sunday. Prosecutors said the killing was preceded by a verbal confrontation that escalated.

Saxony’s governor slammed far-right extremists for using the man’s death as a political tool and for spreading false information online about it. While the influx of migrants to Germany in recent years has resulted in a rise in violent crime, experts have noted that this is largely due to demographic factors: young men, who make up a large share of the migrant population, are generally more likely to commit crimes, whether they’re German or foreign-born.

Governor Michael Kremtscher said authorities would swiftly and thoroughly investigate the killing but will also come down hard on those who had stoked violence in its wake, including attacks on migrants on the sidelines of the protest.

“We will show that we have a strong state,” he told reporters in Dresden, noting that pastfar-rightattacks in the state had demonstrated the need for grassroots efforts to prevent extremism.

Foreign Minister Heiko Maas expressed concern that Germany’s reputation could suffer as a result of violent far-right protests.

“We have to keep in mind that these are pictures that will be seen abroad,” Maas told reporters in Berlin. “But I don’t think that what was seen there even comes close to reflecting the reality in Germany. I firmly believe that the majority of people living in this country want an open and tolerant country.”