BERLIN — A German tabloid that reprinted cartoons from the French satirical paper Charlie Hebdo lampooning the Prophet Mohammed was targeted in a firebombing Sunday, police said.

With security services on high alert after a killing spree in Paris by Islamic extremists, police in the northern German port city of Hamburg said no one was injured in the blaze at the headquarters of the regional daily Hamburger Morgenpost, which caused only slight damage.

“Rocks and then a burning object were thrown through the window,” a police spokesman told AFP. “Two rooms on lower floors were damaged but the fire was put out quickly.”

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The Hamburger Morgenpost, known locally as the MOPO, had splashed the Charlie Hebdo cartoons on its front page after the massacre at the Paris publication, running the headline “This much freedom must be possible!”

Police said the attack had occurred at about 0120 GMT and that two young men seen acting suspiciously near the scene were detained. State security has opened an investigation, a spokesman added.

Whether there was a connection between the Charlie Hebdo cartoons and the attack was the “key question,” the spokesman said, adding that it was “too soon” to know for certain.

Police declined to provide further information about the suspects.

No one at the Hamburger Morgenpost, which has a circulation of around 91,000, could immediately be reached for comment.

“Thick smoke is still hanging in the air, the police are looking for clues,” the newspaper said in its online edition, under the headline “Arson attack on the MOPO – Due to the ‘Charlie Hebdo’ cartoons?”

It published a picture showing firefighters in the courtyard of the building with a caption saying the incendiary device had been hurled into the basement.

Another photo showed charred newspapers from the tabloid’s archive.

It said no one had been in the building at the time.

Hamburg is Germany’s second city, with a population of around 2.4 million.

Media reports said the newspaper’s publishers had ordered private security protection for the building in the western district of Othmarschen after publishing the Charlie Hebdo cartoons.

German news agency DPA quoted a police spokeswoman as saying that the editorial team should be able to continue work in the building as the damage was relatively minor.

“There is no new information, no one has claimed responsibility,” she was quoted as saying.

Two Islamic extremists stormed the offices of Charlie Hebdo on Wednesday, killing 12 people including some of France’s best-loved satirists.

Both men were killed Friday in a standoff with police.

Several German newspapers had published Charlie Hebdo cartoons, including those featuring the Prophet Mohammed, on their front pages Thursday in a gesture of solidarity with the murdered French cartoonists and in defense of free speech.

Chancellor Angela Merkel, due in Paris on Sunday for a massive march in solidarity with the victims, had on Saturday addressed members of her party in Hamburg, which is also one of Germany’s 16 federal states and which is holding elections next month.

She stressed the need for the exchange of security intelligence among Europe’s secret services, particularly among members of the Schengen passport-free zone.

Hamburg’s Islamist scene came to global attention in 2001 when it emerged that three of the suicide hijackers from the September 11 attacks on the United States, including ringleader Mohammed Atta, had lived and studied in the city.

Germany’s Bild am Sonntag newspaper reported earlier that the bloodshed in France could signal the start of a wave of attacks in Europe, citing communications by Islamic State leaders intercepted by US intelligence.

Shortly after the bloodbath in Paris, the US National Security Agency had intercepted communications in which leaders of the jihadist group announced the next wave of attacks, the tabloid said, citing unnamed sources in the US intelligence services.

A 24-year-old German suspected of joining Islamic State jihadists in Syria was arrested Saturday, months after he returned from the war-ravaged country.

German officials estimate around 550 of their citizens have made their way to Syria and Iraq to fight alongside Islamic State, raising fears of attacks on home soil when they return.