BERLIN, Germany (CNN) -- More than 150 German investigators fanned out across Berlin Wednesday, searching dozens of apartments allegedly linked to "potentially violent Islamic extremists," a police spokeswoman told CNN.
The raids centered on a group of approximately 15 suspects -- most of them German citizens -- believed to be plotting bomb attacks in Russia, the release stated. Police said the suspects' actions were being directed by a Berlin-based Islamist organization.
The German capital has been on high alert after al Qaeda and the Taliban released threatening videos shortly before Germany's September 27 national elections. The videos warned voters not to cast their ballots for leaders who want to keep the country's troops in Afghanistan.
But Berlin police said the suspects targeted in Wednesday's raids had no "concrete attack plans in Germany," and the raids had no direct connection to the recent terror threats.
Police believe some of the suspects may have traveled from Germany to the Pakistan-Afghanistan border to train at jihadi camps. Over the past week, three of the suspects were banned from leaving through Berlin's Tegel Airport, and evidence from Wednesday's investigation led authorities to widen that ban to include the other alleged members of the group, police said.
While most of the suspects are German citizens, the group includes Turkish, Algerian, Lebanese, Dutch, and Romanian nationals, police said.
The Berlin raid began shortly after 6 a.m. (0400 GMT) and was still under way at midday, a police spokeswoman said. Investigators seized computers, various memory devices and articles of outdoor clothing from 27 flats, or apartments, in Berlin, the police news release stated.
The raids follow an announcement last week by German prosecutors that a 24-year-old Turkish-German man was arrested "on suspicion of spreading al Qaeda propaganda online and for procuring materials which could be used to make a bomb."
It is unclear if Wednesday's raids were connected to the arrest.
The 24-year-old -- identified only as Adnan V. -- was arrested after searches of a flat in Offenbach and a business in Frankfurt turned up a small amount of an "explosive substance" and a homemade electronic device, prosecutors said in a statement released Friday.
An initial assessment suggested that the items "could be used to ignite explosives," prosecutors said. They added that "there appears to be as yet no direct link" between the al Qaeda and Taliban videos and the Turkish-German man.
CNN's Diana Magnay in Berlin, Germany contributed to this report.