German police said there was no indication that the emailed threat contained any concrete danger.

In a statement, the police said they have assessed that there is no indication that the threat sent by email to ZDF contained any concrete danger. However, the action sparked by the message illustrates that Europe remains on high alert following recent “terror attacks”.

Police searched the ZDF campus with sniffer dogs after receiving the threat on Monday at about 8:20am (06:20 GMT).

A total of 600 ZDF employees were allowed to return to the buildings after they were given the all clear.

Bomb threats were also reported in at least six schools across the country.

Classes were cancelled for hundreds of pupils in the Bavarian cities of Augsburg and Regensburg, Karlsruhe and Mannheim in Baden-Wurttemberg, Solingen in North Rhine Westphalia, and the Thuringian capital Erfurt.

In three cases, the school received the bomb threat via email. But the reason behind the targeting remains unclear. Most of the targeted schools were given the all clear shortly afterwards.

The series of threats is indicative of the growing tension in Europe since the start of the Israel-Gaza war.

The fatal stabbing of a teacher in the northern French city of Arras earlier this month and the shooting of two Swedish football fans in Belgium last week have put authorities on high alert.

In France, a spate of bomb threats has caused the evacuations of schools, airports and other landmarks.

Last week, Interior Minister Gerald Darmanin said authorities had made at least 18 arrests over false bomb threats.