Vojislav Seselj, center, the leader of the ultranationalist Serbian Radical Party, holds a burning NATO flag as he and others gather for a protest in Belgrade, Serbia, Sunday, March 24, 2019. Members of the ultranationalist Serbian Radical Party gathered for a protest on Sunday in the Serbian capital to mark the 20th anniversary of the NATO led bombing campaign against Serbia in 1999. (AP Photo/Marko Drobnjakovic)

BELGRADE, Serbia (AP) — Twenty years after NATO intervened to stop Serbia's onslaught in Kosovo, Belgrade on Sunday commemorated the victims of what it says was an aggression while Kosovo hailed the beginning of its national liberation.

The staunchly opposed views of the two former war foes reflect persisting tensions over Kosovo, a former Serbian province whose 2008 declaration of independence Serbia still does not recognize.

Thousands of people gathered Sunday evening in the southern Serbian city of Nis for the main remembrance event featuring top state officials. President Aleksandar Vucic said in a speech that Serbia will never forget its victims.

"Yes, it was a crime!" Vucic said of the bombing campaign. "No one has been held responsible for these crimes. Serbian civilians, our children, were a permitted target of the NATO aggression."

Anti-NATO sentiments remain high in Serbia even as the country seeks European Union entry. Vucic reiterated Serbia won't join the Western military alliance.

Earlier on Sunday, Serbian far-right supporters burned NATO and EU flags in Belgrade, condemning the 78-day bombing that ended the country's rule over the territory many here view as their nation's historic heartland.

Wreath-lying commemorations also were held throughout the day.

Rights groups say several hundred people died in the NATO bombing, while Serbia says the number of victims was much higher. The bombing also destroyed much of Serbia's infrastructure.

In Kosovo, leaders said NATO's air war brought freedom for their people as they paid their respects to the victims of the 1998-99 war that killed more than 10,000 people.

"It is wonderful that Kosovo's people are free and children can grow up at their home and can go to their schools and that's only thanks to NATO air campaign," Prime Minister Ramush Haradinaj told The Associated Press.

Serbia and Kosovo have been told they must normalize relations in order to advance in their bids to become members of the EU, but the EU-mediated talks have stalled amid tensions.

Several Western embassies in Belgrade on Sunday issued a joint statement of condolence for the victims of the bombing, pledging to "work even harder to contribute to lasting peace and stability to the region."

"We remember March 24 as the day diplomacy failed, and we express our sincere regret for the loss of civilian lives during the events of 1999," said the statement. "We are saddened for all of those who lost their loved ones during the wars of the 1990s."

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Llazar Semini contributed from Tirana, Albania.

Supporters of the ultranationalist Serbian Radical Party march down a street during a protest in Belgrade, Serbia, Sunday, March 24, 2019. Members of the ultranationalist Serbian Radical Party gathered for a protest on Sunday in the Serbian capital to mark the 20th anniversary of the NATO led bombing campaign against Serbia in 1999. The banner reads 'EU + NATO, Enemies of Serbia!' in Serbian Cyrillic letters. (AP Photo/Marko Drobnjakovic)
Vojislav Seselj, front, the leader of the ultranationalist Serbian Radical Party, holds a burning EU flag as he and others gather for a protest in Belgrade, Serbia, Sunday, March 24, 2019. Members of the ultranationalist Serbian Radical Party gathered for a protest on Sunday in the Serbian capital to mark the 20th anniversary of the NATO led bombing campaign against Serbia in 1999. (AP Photo/Marko Drobnjakovic)
Vojislav Seselj, center, the leader of the ultranationalist Serbian Radical Party, speaks to his supporters over a megaphone during a protest in Belgrade, Serbia, Sunday, March 24, 2019. Members of the ultranationalist Serbian Radical Party gathered for a protest on Sunday in the Serbian capital to mark the 20th anniversary of the NATO led bombing campaign against Serbia in 1999. (AP Photo/Marko Drobnjakovic)
Vojislav Seselj, center, the leader of the ultranationalist Serbian Radical Party, and his supporters, march along a street during a protest in Belgrade, Serbia, Sunday, March 24, 2019. Members of the ultranationalist Serbian Radical Party gathered for a protest on Sunday in the Serbian capital to mark the 20th anniversary of the NATO led bombing campaign against Serbia in 1999. The banner reads 'EU + NATO, Enemies of Serbia!' in Serbian Cyrillic letters. (AP Photo/Marko Drobnjakovic)
Kosovo president Hashim Thaci addresses the crowd gathered during the 20th anniversary of the NATO bombing in the village of Glogjan, Kosovo on Sunday, March 24, 2019. Kosovo on Sunday celebrated the 20th anniversary of the NATO bombing as the start of their freedom and independence victory. Many killings from then-Serb leader Slobodan Milosevic were a major factor in NATO's decision to launch an air campaign against Serbia to end Kosovo's 1998-99 war. (AP Photo/Visar Kryeziu)
In this photo provided by the Serbian government, Serbian President Aleksandar Vucic, centre, along with other dignitaries, attend a remembrance ceremony to mark the twentieth anniversary of the 1999 NATO intervention, in Nis, Serbia, Sunday, March 24, 2019.  Twenty years after NATO intervened to stop Serbia's onslaught in Kosovo, Belgrade on Sunday commemorated the victims of what it says was an aggression while Kosovo hailed the beginning of its national liberation. (Serbian Government via AP)
Kosovo prime minister Ramush Haradinaj, right, Rifat Jashari family member of the Jashari family and Kosovo president Hashim Thaci, left, attend the 20th anniversary of the NATO bombing in the village of Glogjan, Kosovo on Sunday, March 24, 2019. Kosovo on Sunday celebrated the 20th anniversary of the NATO bombing as the start of their freedom and independence victory. Many killings from then-Serb leader Slobodan Milosevic were a major factor in NATO's decision to launch an air campaign against Serbia to end Kosovo's 1998-99 war. (AP Photo/Visar Kryeziu)
A Kosovo security force member salutes as Kosovo prime minister Ramush Haradinaj, right, Rifat Jashari family member of the Jashari family and Kosovo president Hashim Thaci, left, attend the 20th anniversary of the NATO bombing in the village of Glogjan, Kosovo on Sunday, March 24, 2019. Kosovo on Sunday celebrated the 20th anniversary of the NATO bombing as the start of their freedom and independence victory. Many killings from then-Serb leader Slobodan Milosevic were a major factor in NATO's decision to launch an air campaign against Serbia to end Kosovo's 1998-99 war. (AP Photo/Visar Kryeziu)
A Kosovo Albanian boy visits the graves at a memorial complex during the 20th anniversary of the NATO bombing in the village of Glogjan, Kosovo on Sunday, March 24, 2019. Kosovo on Sunday celebrated the 20th anniversary of the NATO bombing as the start of their freedom and independence victory. Many killings from then-Serb leader Slobodan Milosevic were a major factor in NATO's decision to launch an air campaign against Serbia to end Kosovo's 1998-99 war. (AP Photo/Visar Kryeziu)
Kosovo prime minister Ramush Hardinaj places flowers on graves during the 20th anniversary of the NATO bombing in the village of Glogjan, Kosovo on Sunday, March 24, 2019. Kosovo on Sunday celebrated the 20th anniversary of the NATO bombing as the start of their freedom and independence victory. Many killings from then-Serb leader Slobodan Milosevic were a major factor in NATO's decision to launch an air campaign against Serbia to end Kosovo's 1998-99 war. (AP Photo/Visar Kryeziu)
Kosovo Albanian children look out from a window at a memorial complex attending the 20th anniversary of the NATO bombing in the village of Glogjan, Kosovo on Sunday, March 24, 2019. Kosovo on Sunday celebrated the 20th anniversary of the NATO bombing as the start of their freedom and independence victory. Many killings from then-Serb leader Slobodan Milosevic were a major factor in NATO's decision to launch an air campaign against Serbia to end Kosovo's 1998-99 war. (AP Photo/Visar Kryeziu)
A member of the Kosovo Security Force honor guard stands at the memorial complex as Kosovo Albanians attend the 20th anniversary of the NATO bombing in the village of Glogjan, Kosovo on Sunday, March 24, 2019. Kosovo on Sunday celebrated the 20th anniversary of the NATO bombing as the start of their freedom and independence victory. Many killings from then-Serb leader Slobodan Milosevic were a major factor in NATO's decision to launch an air campaign against Serbia to end Kosovo's 1998-99 war. (AP Photo/Visar Kryeziu)
Kosovo Albanian children place Albanian flags on the graves at memorial complex during the 20th anniversary of the NATO bombing in the village of Glogjan, Kosovo on Sunday, March 24, 2019. Kosovo on Sunday celebrated the 20th anniversary of the NATO bombing as the start of their freedom and independence victory. Many killings from then-Serb leader Slobodan Milosevic were a major factor in NATO's decision to launch an air campaign against Serbia to end Kosovo's 1998-99 war. (AP Photo/Visar Kryeziu)
Kosovo Albanians arrive to attend the 20th anniversary of the NATO bombing in the village of Glogjan, Kosovo on Sunday, March 24, 2019. Kosovo on Sunday celebrated the 20th anniversary of the NATO bombing as the start of their freedom and independence victory. Many killings from then-Serb leader Slobodan Milosevic were a major factor in NATO's decision to launch an air campaign against Serbia to end Kosovo's 1998-99 war. (AP Photo/Visar Kryeziu)