Russia intensified its attacks in eastern Ukraine on Sunday, while holding events to celebrate a Russian national holiday in territories that Moscow claims are now under its control.

In the city of Severodonetsk in the eastern region of Luhansk, Russian shelling destroyed a bridge amid intense fighting.

Luhansk Governor Serhiy Haidai told local media on Sunday, that he expects Russia to go all out soon to capture Severodonetsk.

Britain's defense ministry said that Russia is gradually seizing territory in and around Severodonetsk.

In Moscow, President Vladimir Putin delivered a speech on Sunday to celebrate Russia Day, which commemorates the country's declaration of sovereignty from the former Soviet Union in 1990.

Putin said that Russians have become keenly aware of how important it is for the fatherland and society to be united. He said unity represents dedication and responsibility for their country.

Celebrations were held in southern and eastern Ukrainian cities that Russia says are now under its control.

In Melitopol in the southeastern region of Zaporizhzhia, a crowd of people gathered at a square holding Russia's national flags.

In areas effectively controlled by pro-Russian forces in the Donetsk and Luhansk regions, separatist and Russian flags were hoisted together along the streets and in public squares.

The events on Sunday followed similar celebrations that took place in Russian-controlled areas on Russia's Victory Day on May 9.

They are apparently aimed at reinforcing its occupation and control of Ukrainian territories.