Nine men - four of them linked to the German capital's "violent Islamist" scene - are being held after multiple early morning raids. Police say they confiscated weapons, electronics and narcotics.
Officers raided six sites across Berlin on Wednesday and detained nine people, who police said were wanted on suspicion of organized drug dealing.
Among the nine arrested were four who police described as linked to the "Islamist spectrum willing to use violence."
As well as weapons found at the addresses, police confiscated drugs and electronic devices.
The arrests were made just a day before former US president Barack Obama was due to address crowds at the four-day Kirchentag festival, alongside German Chancellor Angela Merkel.
In a statement, Berlin police said three of those detained had outstanding arrest warrants, while a fourth was due to appear in court on Wednesday over a previous offense.
The other five men are still under investigation.
Hundreds of officers, including police special units, were deployed for Wednesday's early morning raids, which took place in the Berlin neighborhoods of Neukölln, Köpenick, Mariendorf and Zehlendorf.
The German capital has remained on high alert since Tunisian migrant Anis Amri plowed a stolen truck into a Christmas market last December, killing 12 people.
The attack was later claimed by the self-proclaimed "Islamic State" (IS) group.
Authorities were criticized for failing to arrest and deport Amri, who was a failed asylum seeker and a known drug dealer.
mm/rc (AP, dpa, Reuters)