Ukrainian President Volodymyr Zelensky vowed Thursday that Russia would "not destroy our faith, our sincere belief in Ukraine and God".

Zelensky was speaking as the Russian invasion of Ukraine entered its eighth day, and as news was breaking that the southern Ukrainian city of Kherson, which has a 280,000 population, had fallen to Russian forces.

He said Russia would learn about 'reparations', saying: "Even if you destroy all our Ukrainian cathedrals and churches, you will not destroy our faith, our sincere belief in Ukraine and God, belief in people.

"We will rebuild every single house, every single street, every single city. And we are telling Russia – learn the words 'reparations' and 'contributions'. You will pay back fully to us for what you've done against our state, against our every single Ukrainian."

As Russia's attack on capital city, Kyiv, has become more intense, the southern region of Ukraine has become a critical defensive front against Russia's advances.

Moscow has laid siege to multiple cities there, viewing the region as strategically vital to the success of the entire invasion.

Gaining control of the southern coast would sever the rest of Ukraine from the sea, and would also create a direct connection between Russian-annexed Crimea and the Russian-speaking Donbas region.

Kherson is so far the largest city to fall to Russian forces. It lies on the Dnieper River, giving Russia access to critical canals supplying water to Crimea.

Another large port city in the south is Mariupol, which has a population of 430,000. This city too has been encircled by Russian President Vladimir Putin's forces, and is being shelled relentlessly. Russia's strategy is to also seize Mariupol to establish a direct link between eastern Ukraine and Crimea, both of which have already now fallen into Russian control. Crimea was annexed by Russia in 2014, and is where Putin has launched much of this southern offensive since last week.

Many are now looking with concern to the city of Odesa, which is Ukraine's third-largest city and the country's most important port on the Black Sea. It is considered a major oil terminus. A city of one million Ukrainians, it has so far escaped the worst of the fighting as Russia has not made any significant advances west of Kherson.

The developments in the south of the country come as Ukraine's deputy prime minister insisted that Nato is partially responsible for civilian deaths by refusing to enforce a no-fly zone over Ukraine.

Olha Stefanishyna said, "It is inhumane knowing that the civilian population and kids will be killed by not taking this decision.

"The blood of those civilians - including the mother and father of two kids who were born just yesterday and only today lost their parents in a shelling - is not only on Russian hands."

Stefanishyna apologised for not being diplomatic in her choice of language, but explained that she was speaking while "sitting here in a bomb shelter."

Thus far, Nato members have refused to enforce a no-fly zone over Ukraine due to concerns that it would escalate the conflict and put Western forces in direct combat with the Russians.