The offices of a German newspaper which reprinted Charlie Hebdo cartoons depicting Mohammed has been firebombed. No-one was hurt in the attack.

The Hamburger Morgenpost, a regional daily paper located in the northern port city of Hamburg, printed three Charlie Hebdo cartoons on its front page in the wake of the terrorist attack on the French satirical paper, under the headline “This much freedom must be possible!”

At around 2:20 local time this morning its offices were the subject of an arson attack. “Rocks and then a burning object were thrown through the window,” a police spokesman has said, adding “Two rooms on lower floors were damaged but the fire was put out quickly.” The publisher had ordered extra security for the building following the publication of the cartoons.

According to German news agency DPA, the attack was carried out from within a courtyard within the building. The missiles hit an archive room, destroying some records. It has quoted a police spokesman saying that editorial staff will be able to continue working as the damage was minimal.

The paper’s staff have already updated their online edition, reporting that “Thick smoke is still hanging in the air, the police are looking for clues.”

Police have also said that they have detained two people in connection with the attack, and that state security forces are investigating. On the “key question” of whether the attack was connected to the Charlie Hebdo cartoons, the police said that it was “too soon” to know for certain.

There are growing concerns that the Charlie Hebdo attacks, and the response, could unleash a wave of similar attacks across Europe. According to German newspaper Bild, the US National Security Agency has intercepted communications from Islamic State leaders announcing the next wave, citing unnamed sources in the US intelligence agencies.

This morning a video emerged of Amedy Coulibaly, the terrorist shot dead by police after killing four hostages in a kosher supermarket, pledging allegiance to Islamic State.