Croatian police confirmed that a mass grave from the Second World War was found on the outskirts of Zagreb, local media reported.
The grave is believed to contain remains of 17 men, possibly of Croatian and German soldiers executed by Yugoslav Communists at the end of the war, the Vecernji List online edition reported.
Police said forensic experts were investigating the site.
A civic action leader and head of the Responsible Croatian Society organisation, Ivica Relkovic, told Vecernji that he located the site through eyewitness reports who recalled that Partisans had rounded up people at that spot. He then provided the map to police.
He said five other graves in the immediate vicinity contained the remains of at least 50 other victims. All were believed to have been shot by the Communist Partisans.
Relkovic believed that the victims were members of a Croatian army unit captured and executed by Partisans between May 8 and 9, 1945.
Croatia broke off from Yugoslavia in 1941 and sided with Hitler's Germany. Following the victory of Yugoslav communists under Marshall Tito, Yugoslavia's later long-term leader, the country returned to the union under Belgrade's sovereignty.
Croatia again split from Yugoslavia in 1991.
Tito's regime summarily executed thousands of German and other foreign soldiers, along with many more local men accused of collaborating with the enemy.
Croatian authorities were still working on a massive grave at Harnica, 50 km north-west of Zagreb, where an estimated 4,500 bodies of Croatian and German troops from the so-called Blue Division were executed and buried in 1945.
That grave, accidentaly exposed during construction work, is just one of the many mass graves left by the Partisans, Croatian officials said.
Interior Minister Tomislav Karamarko last year said the number of mass graves from the era across former Yugoslavia was probably greater than 1,000.
He said there are 600 mass graves in Slovenia, 840 in Croatia, 90 in Bosnia and "who knows how many more" strewn across the entire region.