A 37-year-old Romanian and a 54-year-old Greek suspect were arrested in Hamburg and in a Greek village "on suspicion of attempted sabotage of a defence vessel", they said in a statement.

The men are accused of putting more than 20 kilograms (about 40 pounds) of grit into a ship's engine block, puncturing water supply lines, removing caps from fuel tanks, and deactivating electronic safety switches.

"Had the acts of sabotage gone undetected, they would have led to significant damage to the ships or, at the very least, delayed their departure, thereby potentially endangering the security of the Federal Republic of Germany and troops' operational effectiveness," prosecutors said.

Prosecutors said they were still investigating the background to the alleged acts of sabotage.

Germany and other NATO members across Europe are on high alert over suspected Russian espionage, drone surveillance and sabotage.