Croatian Flash offensive on May 1, 1995, is marked differently on two sides of the border between former republics of the same country: Croats celebrated the beginning of the liberation of the territory held by rebel Serbs, while the Serbs commemorate their victims.
In the Belgrade St. Marko church the clergy held a memorial service, while in the western Slavonia's town of Okucani, Croatian President Kolinda Grabar-Kitarovic and other top country's officials joined the celebration of the Flash operation.
The Croatian Army launched the battle in its western chunk of Slavonia and defeated the Serb forces in three days. Many locals fled the region.
The offensive came in the later stage of the Croatian War of Independence 1991-1995.
The last organised RSK resistance formally ceased on May 3, with the majority of troops surrendering, but mopping-up operations continued for another two weeks.
According to data from the Serb Documentation-Informative Centre Veritas, 283 people were killed or missing during the operation, mostly the Serbs, 114 of whom were civilians, while 1,450 soldiers were captured, and reportedly tortured.
Croatia's official data say that about 7,200 troops and police officers took part in the liberation of Western Slavonia, of whom 42 were killed and 162 wounded. It was the first time during the 1991-1995 Homeland War that the Croatian Air Force had used airstrikes on a larger scale, and the enemy was further surprised by tanks that were brought in by rail and deployed in combat.
"Operation Flash marked the beginning of the liberation of Croatian territory and the re-integration of Croatia," Grabar-Kitarovic said, adding her thoughts were with the families of all defenders who had been killed or missing.
She was also asked to comment on Serb victims killed during Operation Flash.
"We regret every victim," Grabar-Kitarovic replied.
The commemoration was also held in Gradiska, a town in Republika Srpska, the Serb entity in Bosnia and Herzegovina, where there is a monument to the Serb victims from western Slavonia.
Milorad Dodik, the Chairman of the Bosnia tripartite rotating Presidency, said that "at the end of last century, the calamity and ethnic cleansing of the Serbs happened in Croatia and Bosnian Federation (the second Bosnian entity shared by Bosniaks and Croats)."
"Unfortunately," Dodik added, "the pressure on the life and national identity of the Serbs still exists."