KYIV, Dec 19 (AFP) - President Volodymyr Zelenskiy said protecting Ukraine's borders was a "constant priority" and his country was ready for all possible scenarios with Russia and its ally Belarus, which Kyiv has warned could be drawn into the 10-month conflict.

Zelenskiy, in his nightly video address to Ukrainians, also issued a fresh appeal to Western nations to provide Kyiv with better air defences as "one of the most powerful" steps to halt the Russian invasion.

Early on Monday, air raid warnings again rung out over Kyiv and eastern Ukraine, with videos of blasts and air defence systems shared on social media.

"Protecting our border, both with Russia and Belarus - is our constant priority," Zelenskiy said after a meeting on Sunday of Ukraine's top military command. "We are preparing for all possible defence scenarios."

Zelenskiy was speaking on the eve of a visit to Belarus by Russian President Vladimir Putin amid discussion of a possible new Russian offensive and suggestions it could originate in Belarus.

Officials in Kyiv have warned for months that Belarus could join Russian forces and serve as a launching pad for a new attack to form a second front in the war.

Whatever Belarusian President Alexander Lukashenko might be persuaded to do for Russia "this will not help them, just like all the other sick ideas in this war against Ukraine and Ukrainians," Zelenskiy said.

Belarus is one of Russia's closest allies and Lukashenko allowed his country's territory to be used to embark on the Feb. 24 invasion of Ukraine. But he has said repeatedly that he has no intention of sending his country's troops into Ukraine.