The grave contains the remains of Croatian prisoners of war that were murdered after the war.
There were also prison camps, where Croatian prisoners of war and civilians were kept by Serbian authorities.
At the same time, the Ovčara massacre happened, in which the Serb forces executed 264 Croatian prisoners of war and civilians.
The island was the site of a massacre of 204 German and Croatian prisoners of war by Yugoslav Partisans in May 1945.
Red Cross officials have freed 2,009 Muslim and Croatian prisoners from the Manjaca camp so far this week, including 1,001 today, the statement said.
It contains the remains of a group of Croatian prisoners of war that tried to pass photos to local residents before being taken away and murdered in May 1945.
Ovčara was also a Serbian transit camp for Croatian prisoners from October to December 1991.
Earlier in the day, a similar exchange involving more than 5,000 Muslim and Croatian prisoners was also postponed indefinitely.
At that time numerous Croatian prisoners of war were held at the camp.
During Yugoslav wars, some Croatian prisoners of war were kept in this prison.