Four German members of a hardcore neo-Nazi terror cell have been charged with planning to bomb refugee shelters and assassinate Salafi clerics, media report. It comes alongside warnings by German politicians far-right violence against refugees is on the rise.

Federal prosecutor Peter Frank filed criminal charges against four suspects of a neo-Nazi terror cell called “Oldschool Society” on Wednesday, according to German media.

Their Facebook cover at the time was an infamous photo of an entrance to Auschwitz concentration camp reading “Arbeit macht frei” (“Work will make you free”), Spiegel reports. They also posted a YouTube recruitment advertisement saying, “We need every man, every woman to fight together for our homeland.”

The "Oldschool Society" also used WhatsApp and Telegram messengers for communication, and set up a clandestine HQ dubbed “Privy council.”

By May 2015, the neo-Nazi group was reportedly ready to carry out “a couple of actions” against refugee shelters, including one in the German town of Borna. It ordered its members to wear “black, casual clothes,” according to wiretapped phone conversations cited by Der Spiegel.

At the same time, the Oldschool Society allegedly sent Markus W. and Denise Vanessa G. to the Czech Republic, where they were tasked with buying large amount of explosive materials, while another suspect, Andreas H., worked on how to increase the power of their nail bombs.

The terror group members were detained in May 2015 following an operation by dozens of GSG 9 elite counterterrorist operatives, who simultaneously raided the homes of 10 neo-Nazis, including those of Andreas H., Markus W., Denise Vanessa G. and Olaf O. Explosive devices labeled “Cobra” and “Viper” as well as baseball bats were found in the suspects’ locations.

“That was quite a dangerous group,” an unnamed investigator told journalists. “It could quickly grow up and turn into a terrorist community.”