Berlin has said reparations to Greece were settled in 1960 as part of an agreement with several European governments.
But successive Greek administrations have invoked the issue in recent years amid flaring tempers between debt-mired Athens and the eurozone's paymaster, which has dictated tough austerity terms in return for Greece's three European bailouts.
"[Greece] will do whatever is necessary, mainly at a diplomatic level, and if necessary, at a legal level," Tsipras said during a visit to Kommeno, a village wiped out by Nazi soldiers in 1943.
"Greece and its people do not forget the slaughter and war crimes of the Nazi army and demands a tangible recognition by the German government, even one that is 73 years late," he added.
In Kommeno, northwestern Greece, Nazi troops killed 317 civilians on August 16, 1943. They later carried out similar atrocities at the villages of Kalavryta and Distomo.
A special Greek parliamentary committee looking into the war reparations issue recently came to a total of €269.5 billion, including a forced loan of €10.3 billion, but not counting loss of life and injury.
The committee report, seen by AFP, is to be discussed by parliament early next month.