European journalists were on edge Sunday following an attack on a German publication that reprinted controversial cartoons in the wake of the deadly terror attack on French satirical magazine Charlie Hebdo.

Two suspects were arrested in the firebombing of a Hamburg tabloid that had splashed three Charlie Hebdo cartoons on its front page in response to Wednesday’s slaughter in Paris, according to cops.

“This much freedom must be possible!” the Hamburger Morgenpost headline screamed.

Rocks and a “burning object” were tossed through a window at the paper’s headquarters, damaging two lower-level offices at around 2:20 a.m. local time, a police spokesman said. No injuries were reported.

The suspects, ages 35 and 39, were nabbed because they were seen acting suspiciously, AFP reported.

Morgenpost Editor in Chief Frank Niggemeier said the paper was “shocked that something like this could happen in a cosmopolitan and liberal city like Hamburg” and vowed to publish Monday’s edition.

Meanwhile, staffers at a Belgian newspaper that also reprinted Charlie Hebdo cartoons fled their offices following a bomb threat Sunday afternoon.

The scare at the headquarters of the French-language daily Le Soir came as 20,000 people marched silently through the Belgian capital to protest the Charlie Hebdo massacre and related terror attacks around Paris.

“An anonymous caller made threats against the editorial side of the paper, after which it was decided to evacuate the building,” Le Soir foreign-news editor Maroun Labaki told Belga News Agency.

A reporter for the paper tweeted that the caller warned a bomb was “going to go off in your newsroom,” according to AFP.

Cops closed the roads around Le Soir’s headquarters — where posters saying, “JE SUIS CHARLIE,” hung in the windows — but no violence was reported.