Germany's Cologne-Wahn military base has been sealed off for a couple of hours on Wednesday after a suspected act of sabotage against its water supply.

According to the press release from the German military, a guard detected a hole in the fence near the water processing plant of the barracks early on Wednesday morning. A search of the premises did not turn up any trespassers.

Employees at the base were told not to drink the tap water, as authorities investigated possible contamination. The barracks will be supplied with water by canister until test results are available.

Police, military police, and the military intelligence agency MAD are all looking into the alleged crime, authorities said.

"We have our reasons for taking this action, and we take the case seriously,"  the Territorial Command said in the press release.

The base near Cologne-Bonn airport employs 4,300 soldiers and 1,200 civilians and is also home to a fleet of military aircraft used by Chancellor Olaf Scholz for international travel.

Security levels raised at NATO air base in Geilenkirchen

Security levels at a NATO air base in the town of Geilenkirchen, also in the same state as Cologne, were raised following the incident in Cologne.

"The base (in Geilenkirchen) was at no time sealed off. We checked the water, it is okay, and the base is accessible," a NATO spokesperson in Geilenkirchen was quoted by Reuters as saying later Wednesday.

A German military spokesperson had previously said that the base in Geilenkirchen had been sealed off. 

Increasing attacks by Russian intelligence

It could not be immediately confirmed who had carried out the alleged sabotage, but NATO Secretary-General Jens Stoltenberg had recently warned that a pattern was evolving of Russian intelligence becoming more bold in its operations against member states. This went for cyberattacks as well as field operations.

Poland, the UK, and the Czech Republic have reported similar incidents in the past months.

rm, es, ch/dj (dpa, Reuters)