German police announced late on Sunday that a gang of about 20 people attacked six Pakistanis and injured two while another group of five people attacked and injured one Syrian man in Cologne amid an increase in tensions following assaults on New Year's Eve assaults that have been widely attributed to foreigners.
The German newspaper Express reported that the assailants were members of rocker and hooligan gangs who organised on social media to meet in Cologne to launch a "manhunt" of foreigners.
More than 600 criminal complaints were recorded related to assaults on women in Cologne and other German cities.
The latest incidents have ignited criticisms on Germany's open-door policy for refugees and also triggered a discussion over harsher penalties for refugees who violate the law, such as speeding up the deportation process and increasing security measures.
A German state interior minister on Monday accused Cologne police of making "very serious" mistakes in handling the New Year's Eve violence.
Police said it is being investigated whether the gang attacks were racially motivated and whether the incident had any connection with the New Year assaults.
Germany has accepted almost 1.1 million refugees this year and the country's federal states are planning to allot a budget of about 17 billion euros ($17.58 billion) for the accommodation of refugees in 2016.
However, attacks against refugee shelters more than quadrupled from 114 in 2014 to 505 in 2015. There were only 18 such attacks in 2011.