Tens of thousands of Croatians gathered in the eastern city of Vukovar Sunday to commemorate one of the bloodiest episode of the Balkan nation's 1990s war for independence.

Prime Minister Zoran Milanovic and President Ivo Josipovic attended the memorial ceremony, which drew about 50,000 people.

Also present was general Mladen Markac, whose conviction for war crimes was overturned on appeal last Friday by the International Criminal Tribunal for the Former Yugoslavia (ICTY).

"My heart told me that I have to come here, and I did," Markac told national television.

Mourners gathered at the town's hospital, a wartime symbol of resistance, then proceeded to a memorial cemetery where they lit candles and laid wreaths for those killed during and after the town's three-month siege.

"We here again to remember the Vukovar suffering, to remember innocent victims and promise our children that anything similar will never happen again," Josipovic said.

The fall of Vukovar to the Serbs in 1991 marked the start of Croatia's war of independence from the former Yugoslavia, which claimed around 20,000 lives.

But the battle for the city was crucial for Croatia as it stalled Yugoslav forces long enough to give Zagreb time to arm and prepare troops.

During the siege of the city, some 1,600 defenders and civilians were killed and the town was virtually razed to the ground. Afterwards, Yugoslav forces expelled some 22,000 Croats and other non-Serbs, almost half of its population.

Some of those attending, including veterans of the conflict, carried Croatian flags and a giant banner with photos of Markac and Ante Gotovina, the other general freed on appeal by the tribunal.

Both Gotovina and Markac had already received a hero's welcome home after The Hague-based tribunal acquitted them on Friday.

Markac and Gotovina, were initially convicted and last year sentenced to 24 and 18 years in jail respectively for war crimes against ethnic Serbs.

Croatians have been euphoric over their successful appeal at the Hague-based court and the mayor of Vukovar Zeljko Sabo invited both men to attend Sunday's commemoration, though Gotovina did not appear.

In 1991, about 400 wounded Croats and other non-Serbs were evacuated from the hospital by the Yugoslav People's Army.

Soldiers then bused some 260 evacuees to a secluded pig farm a few kilometres away, where they were beaten, killed and buried in mass graves.

The ICTY convicted two Serb officers, Mile Mrksic and Veselin Sljivancanin, for the massacre and sentenced them to 20 and 10 years in prison, respectively.

Croatian Serb former rebel leader and the last Yugoslav war crimes fugitive Goran Hadzic, whose trial before the ICTY opened last month, have also been charged for the massacre of Vukovar civilians.

After the war, Vukovar was put under UN administration and reintegrated into Croatia in 1998.

More than 400 people from the Vukovar area are still listed as missing.