The find in a forest near the town of Popricani, about 350 kilometers (220 kilometers) northeast of Bucharest, contains the bodies of men, women and children who were shot in 1941, the Elie Wiesel National Institute for the Study of the Holocaust in Romania said in a statement.
On Friday, riot police sealed off the area, not allowing anyone near the site, local reporters told The Associated Press.
The find offers evidence of pogroms against Jews in the region, scholars say, campaigns that were long minimized in a country whose official history taught that Germans were the sole perpetrators of the Holocaust.
Sketchy reports about the possibility of a mass grave in the forest began to appear in 2002, and local authorities began an investigation, which was suspended in the fall after nothing was found. Experts resumed the investigation at the site and began interviewing witnesses again in 2009, according to Romanian historian Adrian Cioflanca.