ODESA, Ukraine -- Security was beefed up in Ukraine's Black Sea port city of Odesa during ceremonies to commemorate 48 people killed in 2014 during clashes between pro-Ukrainian and pro-Russian demonstrators.
More than 1,000 police and security officers were deployed on May 2 near Kulikovo Field in Odesa and the Labor Unions building, where the deadly violence took place four years earlier.
Hundreds of pro-Russian activists gathered on the site and recited prayers to commemorate the victims.
They also released dozens of helium-filled black balloons with the inscription "Odesa, May 2, We Remember."
Hundreds of pro-Ukrainian activists also came to the site and chanted "Glory to Ukraine!" as the balloons were released.
The two opposing groups exchanged insults, but police prevented fresh violence.
According to Odesa regional police, some 2,500 people passed through metal detectors to enter the site.
The Ukrainian Security Service (SBU) said earlier that communist and Nazi symbols were prohibited at the commemoration events.
Right-wing Ukrainian nationalist groups planned to hold what they called a March of the Ukrainian Order later on May 2.
Since 2014, pro-Russian and pro-Ukrainian activists have returned to the site on May 2 to commemorate the victims. Fighting broke out between the groups there in 2015, 2016, and 2017.
Odesa's regional police said that 2,500 police and National Guard troops were patrolling the streets of Odesa.
The violence in 2014 broke out in Odesa in the wake of Russia's annexation of Crimea and after Moscow began supporting pro-Russian separatists in eastern Ukraine.
As pro-Russian and pro-Ukrainian marchers marched in the city center, clashes erupted between the opposing sides and gunfire killed several people.
Later, violence broke out at Kulikovo Field and a fire gutted the Labor Unions building, where pro-Russian demonstrators had taken shelter.
It remains unclear how the fire started.
Supporters of Ukraine's government were seen throwing firebombs at the building.
But official accounts by Ukrainian authorities say those inside the building may have caused the blaze by throwing firebombs from the roof.
Forty-two people were killed by the fire in the building.