German police are treating the latest in a series of attacks on asylum seekers as "anti-foreigner crimes" and believe that they were organized via social media, a spokesman said on Monday.
The fact that right-wing extremists were strategically using the internet to plan indiscriminate attacks against "non-Germans" is "an alarming signal that we are taking very seriously," police spokesman Norbert Wagner said.
Wagner was referring to two incidents that took place in Cologne on Sunday in which six Pakistanis and one Syrian asylum seeker were attacked by groups of "right-wing extremists from the hooligan, rocker and bouncer scenes."
Two of the six Pakistanis were brought to hospital with serious injuries after as many as 20 people attacked them at just before 7 pm (1800 GMT) on Sunday near Cologne's main train station.
About 20 minutes later, a group of five men attacked a Syrian man at a nearby location. He was injured but didn't require medical treatment.
Police stopped and searched 153 people before and after the attacks after receiving tip-offs that right-wing extremists were forming vigilante groups to police the streets following the mass sexual violence in Cologne and other German cities.
Though Chancellor Angela Merkel and several politicians from her coalition have warned against blanket suspicion of foreigners - many of whom are seeking refuge from war - Muslim groups have reported a spike in anti-Islam sentiment.
"We are witnessing a new dimension of hate," Aiman Mazyek, the head of the Central Council for Muslims in Germany, told regional newspaper Koelner Stadtanzeiger on Monday, adding that the number of attacks against its members were on the rise.
Separately, a Jewish man wearing a skullcap in the northern German town of Puttgarden was attacked and robbed late on Sunday by two refugees from Syria and Afghanistan respectively.
The two men, who were arrested by police shortly after the attack, had been trying unsuccessfully to cross Germany's northern border into Denmark.
The news comes after comments from the interior minister of North Rhine Westphalia, where Cologne is located, confirming that the perpetrators were "almost exclusively" of a North African or Arab background further inflamed an ongoing migration debate.
A total of 553 police complaints - 45 per cent of them related to sexual violence - have been filed in Cologne, prompting politicians to call for increased security, the expulsion of criminal asylum seekers and the reduction of migrant flows going forward.
Of the 19 suspects identified by police, 10 are asylum seekers and nine are in Germany illegally, according to a report submitted to a parliamentary committee looking into the crimes. None have residences in Cologne and four are currently in police custody.
Later Monday, pro- and anti-immigrant groups staged competing demonstrations in the eastern city of Leipzig. Pro-migrant groups formed a chain of lights in solidarity with the refugees who have come to Germany in recent months, drawing between 2,300 and 2,800 people, organizers said.
However, demonstrators from the Legida group, an offshoot of the Dresden anti-foreigner group Pegida, said they had gathered between 1,500 and 2,000 members for their demonstration.
In Postdam later Monday clashes broke out between Pegida marchers and a counterdemonstration held by people opposed to the movement. Police said the Pegida opponents tried to attack the Pegida march.
Police used pepper spray after stones and firecrackers were thrown, traffic signs were ripped from their bases and garbage cans were flipped over.
Hundreds of people had gathered earlier in Potsdam's city centre for a demonstration against Pegida that for the most part was peaceful. About 100 Pegida sympathizers held their demonstration a few hundred metres away on another plaza.