German police say a Hamburg newspaper hit by arsonists may have been targeted for its reprinting of satirical cartoons from French newspaper Charlie Hebdo.

An incendiary device was thrown into a building of the Hamburger Morgenpost Daily over the weekend, setting some documents on fire.

Two people have been arrested.

Hamburg police spokesperson Mirko Streiber.

"We don't know anything about the motivations behind the attack. Many people are speculating about it, and it is quite obvious that there is a connection with the reporting of the events in France, perhaps this has something to do with it."

Hamburger Morgenpost newspaper had reprinted cartoons from Charlie Hebdo in a show of solidarity with the French weekly following the deadly attack at its Paris office last week.

The newspaper says there were no people in the building at the time of the attack, and investigators were checking for any connection with the cartoons.

A security alert in Hamburg has not been enforced, as police say the motivations behind the attack on Hamburger Morgenpost have not yet been determined.

But in Berlin, security was stepped up outside the offices of some of the most prominent newspapers in the country.

As with other west European countries, Germany is struggling to stop the radicalization of disaffected young Muslims, some of whom want to become jihadist insurgents in Syria or Iraq.