Germany can expect “further significant attacks” after a Berlin Christmas market was hit on Monday and a “dangerous criminal” could still be on the run, top police bosses have warned.

Berlin police chief Klaus Kandt instructed his countrymen on Tuesday to be “particularly vigilant” as the suspected terrorist behind the attack could be armed and on the run, and the head of the federal criminal police office, Holger Münch, said Germany remained on “high alert”.

Islamic State has also claimed the attack – the worst terrorist atrocity on German soil since 1980 – describing the driver of the truck as “a soldier of” of their jihadi terror group.

This morning, police revealed they are now hunting a 24-year-old Tunisian immigrant named as Anis A., after a 23-year-old Pakistani ‘refugee’ was released last night.

“We need to work on the assumption that an armed perpetrator is still on the loose. As a result of this we are on high alert,” Mr. Münch said at a press conference delivered by federal prosecutors.

“Currently we have one suspect but we are not sure whether he is the perpetrator and we don’t know whether there is only one. We have not found the weapon and that leads us to being in a high state of alert.

“Our investigations are on-going to see whether there are other perpetrators that we need to arrest.”

The warning came as Germany’s top prosecutor, Peter Frank, said more than one person could have carried out the massacre.

He had also conceded that the then-suspect in custody “may not have been the perpetrator or belong to the group of perpetrators” before the Pakistani migrant was released hours later.

Yesterday, German police said they were “working on the assumption that the truck was steered deliberately into the crowd”, with Chancellor Angela Merkel saying it must be “presumed” to be a terror attack.

The anti mass-migration AfD party did not mince their words. “Germany is no longer safe,” AfD co-chairman Frauke Petry commented.

Adding: “We must be under no illusions. The breeding ground in which such acts can flourish has been negligently and systematically imported over the past year and a half.”

In Washington D.C., State Department spokesman John Kirby said the attack “bears the hallmarks of previous terror attacks,” but U.S. officials didn’t have enough information to back up Islamic State’s claim of responsibility.

“There is no direct evidence of a tie or a link to a terrorist organization,” he said, according to USA Today.