The Cologne-Wahn base "has been locked down because there is a suspicion of an attempted intrusion and a suspicion of sabotage," defence ministry spokesman Colonel Arne Collatz told reporters in Berlin.

Der Spiegel magazine reported that police and the German military's counter-intelligence service were investigating an apparent break-in, with its sources saying a hole in the fence had been discovered.

Soldiers and civilians on the Bundeswehr base have been advised not to drink the tap water, Spiegel added, over concerns that the water supply "may be contaminated".

The Cologne-Wahn base, located near Cologne-Bonn airport, houses several military and civilian facilities of the German armed forces as well as aircraft used by Chancellor Olaf Scholz and his ministers for government travel.

Some 4,300 soldiers and 1,200 civilians work at the site, according to Spiegel.

The base is also an important hub for military support for Ukraine. Ukrainian soldiers regularly fly home from there, via Poland, after receiving training in Germany, Spiegel added.