After the explosion at a party office of the left in Oberhausen, the police found evidence of a homemade explosive device, according to information from the German Press Agency.
Investigators said that a so-called unconventional explosive and incendiary device (USBV) could be responsible - built, among other things, with "lightning explosives" such as those found in fireworks.
There are no indications of possible perpetrators.
At around 3:20 a.m., the explosion destroyed the windows of the party office and neighboring shops, among other things.
The parliamentary group leader of the Left in Oberhausen, Yusuf Karacelik, said on Tuesday, according to a written statement: "We are assuming a targeted attack from the right." Karacelik spoke to the German Press Agency of a "right-wing terrorist attack".
The federal chairwoman of the left, Janine Wissler, and the North Rhine-Westphalian party leader Jules El-Khatib, in their own words, suspect a right-wing extremist background.
The investigators are also pursuing other possible leads.
Several members of the left from Oberhausen took part in a demonstration in Berlin at the weekend, which was directed against Germany's rearmament because of the Ukraine war.
State security determined
A police spokeswoman emphasized that investigations are being carried out in all directions.
Because a politically motivated act cannot be ruled out, the Essen police department is investigating together with the Duisburg public prosecutor's office.
Experts from the State Criminal Police Office were also on site on Tuesday.
In addition to the party's office on Friedensplatz in Oberhausen, a hairdresser's shop and a travel agency were also badly damaged by the explosion.
Windows shattered, interior fittings were partly destroyed.
"The property damage is significant," said the police spokeswoman.
Investigators are now looking for witnesses.
The left called for a "rally against right-wing terror" at the crime scene in Oberhausen, which the police said about 250 people attended on Tuesday evening.
The demo was peaceful.
Slogans such as "All together against fascism", "Oppose right-wing violence" and "Against intellectual arsonists" were on banners.