Sandor Kepiro, 97, stands accused of murdering 36 people during a 1942 operation in the Yugoslav town of Novi Sad that claimed the lives of some 4,200 civilians.
But in court Mr Kepiro, who declared himself fit to stand trial, dismissed the charges.
"I am innocent and I am here on trumped-up charges," he said. "This trial is a terrible thing. There is no basis to this, everything is based on lies."
During the war Mr Kepiro, a gendarme captain in Hungary's fascist forces, took part in the Novi Sad raid but has always maintained that while he helped arrest civilians he took no part on the bloodletting. Hundreds of Serbs, Jews and Roma were taken to the banks of the Danube and shot or thrown into the frozen river alive by Hungarian forces in apparent revenge for partisan attacks.
For his alleged role in the massacre Mr Kepiro at one time topped the Wiesenthal Center's most-wanted Nazis list.
RELATED ARTICLES
Germany 'tried to influence Adolf Eichmann trial' 18 Apr 2011
Pope visits memorial to Nazi victims in Rome 27 Mar 2011
"It's clear that this is one of the last major trials of Holocaust-era war criminal suspects," Efraim Zuroff, chief Nazi hunter at the Wiesenthal Center.
Meanwhile in Rome, Ernst Pinstor, an ex-Wehrmacht captain, Fritz Jauss, a former warrant officer and Johann Riss, a former sergeant, were accused of killing 184 men, women and children in the Tuscan village of Padule di Fucecchio, near Florence, in August 1944.
Marco De Paolis, a military prosecutor, told the court that the three men, who are all in their nineties and live in Germany, had never shown any remorse over their alleged roles in the atrocity. The trio deny the allegations.
The killings took place a day after an SS division killed 560 people in the nearby village of Sant'Anna di Stazzema, the backdrop to 'Miracle at St. Anna', a 2008 film by Spike Lee, the American director.