A military base in the German city of Cologne was placed on lockdown on Wednesday over fears of a potential act of sabotage, Der Spiegel has reported. A spokesperson for the German Defense Ministry has confirmed that security services have launched an investigation.

In recent months, several Western media outlets as well as officials have alleged that Russia has been stepping up efforts to conduct acts of sabotage on European soil. Moscow’s presumed endgame is to disrupt the delivery of Western weapons to Ukraine and the training of Kiev’s troops abroad.

Moscow has consistently dismissed the allegations as “not serious” and “unfounded.”

In its article on Wednesday, Der Spiegel reported that the Bundeswehr barracks had been completely sealed off, with police and military counter-intelligence services looking into a potential case of unauthorized entry.

According to the media outlet, it is suspected that saboteurs might have contaminated water supply at the military facility. The outlet cited presumed internal instructions disseminated among the personnel warning against using water from the base’s utility system.

The article alleged that military personnel at the base had also been instructed to be on the lookout for any unknown individuals and to report “suspicious behavior” on the grounds. Der Spiegel speculated that security services may be searching the base for potential saboteurs, with a suspicious individual allegedly sighted near the fence that encloses the complex. The individual is understood to have fled after being detected.

The media outlet also reported that, on closer inspection by military police, an opening in the fence had been uncovered.

According to the article, cases of gastrointestinal disease have been reported at the base of late, though it is not clear whether these had anything to do with water supply at the installation.

The barracks in Cologne is where several Bundeswehr command units are stationed. On top of that, the installation houses the German Air Force, with Cologne Airport immediately adjacent to the base, Der Spiegel noted. According to its estimates, a total of 5,500 military and civilian personnel work at the military facility.

The base is also said to be a key hub for Ukrainian service members returning home after receiving military training in Europe.

Back in April, the German Prosecutor General’s Office reported that two German-Russian dual nationals had been arrested on suspicion of planning to sabotage local military infrastructure.

Around the same time, the head of German domestic intelligence, Thomas Haldenwang, warned that the risk of acts of sabotage had “significantly increased” in the country.