Marko Strovs, who heads the government's commission for exhuming mass graves, told The Associated Press that researchers examined a pit in a forest near the town of Prevalje in the country's northeast last week and found the remains.
"Based on what we've heard from local people and what we've seen so far, there could be about 700 bodies buried inside," Strovs said.
Thousands of Nazi collaborators were executed by communist-backed antifascists after the war; in many cases, victims also included innocent civilians. Communist authorities in the former Yugoslavia, which included Slovenia until it dissolved in 1991, played down or denied postwar slayings, though other mass graves have since been found.
Strovs said the 70-foot-long by 10-feet-wide pit contains the bodies of men and women. Initial findings are that their hands were tied behind their backs.
"Some of the victims were shot; some seem to have been killed by a tool, possibly an ax," he said, adding that at least some of the victims were civilians, based on the types of shoes they were wearing.
Details of the 1945 slaying in the Prevalje forest have circulated in the area for years, after a boy reportedly witnessed the executions while hiding in a tree. He has since died, but recent floods caused a landslide that revealed some of the bones, prompting last week's probe. Some of the victims were likely from neighboring Austria, local residents said.
The process of exhumation will begin once a district prosecutor approves it.
The discovery follows several others. In 2003, a farmer unearthed remains in eastern Slovenia, where villagers claimed hundreds of Nazi soldiers and civilians were killed and buried. In 1999, experts found a grave with about 1,000 bodied while building a highway near Maribor in northeastern Slovenia.
Slovenia was a route to the West for many from Yugoslavia who tried to flee post-war reprisals. Many were turned back from Austria and killed as they crossed back over the border.