The ammunition disappeared "from the trailer of the civilian carrier's transport vehicle, which had been parked overnight", the spokesman said.

German media reported that boxes containing about 20,000 rounds were stolen from the truck after it was parked outside a hotel near the eastern city of Magdeburg.

An initial check revealed that about 10,000 rounds of combat ammunition for pistols, 9,900 rounds of blank manoeuvre ammunition for assault rifles and so-called smoke ammunition were stolen, said news weekly Der Spiegel.

The driver had apparently spontaneously decided to spend the night in the hotel in the town of Burg, according to the magazine.

The fact that the ammunition was missing was discovered upon delivery of the rest of the shipment to the barracks it was destined for, the army spokesman said.

"The theft was immediately reported to the relevant security and investigative authorities. We take this incident very seriously and are conducting a thorough investigation," he said.

A police spokeswoman in the nearby town of Stendal confirmed to AFP that an investigation had been opened but gave no further details.

Armed forces sources told Der Spiegel the incident was unlikely to have been a "random robbery".

"Instead, they fear that the ammunition transport was being watched and that the perpetrators struck when the driver made the unplanned stop in Burg," the news magazine said.

The contractor had broken protocol by allowing the cargo to be transported by only one driver, when normally there should have been two, according to Der Spiegel.

Germany has vowed to revive its long-neglected armed forces in the face of an emboldened Russia and last week approved a budget for 2026 that includes vast new debt for defence spending.

The conservative-led ruling coalition has also agreed on a new military service model to attract more recruits to the armed forces, or Bundeswehr.