Ukrainian forces are digging new fortifications and preparing battle plans along the entire frontline as spring, and a probable new Russian advance, nears.

But this may be the last spring for occupying Russian forces.

"Spring and early summer will be decisive in the war. If the great Russian offensive planned for this time fails, it will be the downfall of Russia and Putin," said Vadym Skibitsky, the deputy head of Ukrainian military intelligence.

Skinitysky added that Ukraine believes Russia is planning a new offensive in the spring or early summer. The Institute for the Study of War thinks that such an offensive is more likely to come from the occupied territories of Luhansk and Donetsk than from Belarus, as some have feared.

Still, the possibility of an attack by Belarus should not be dismissed entirely — all the more so because, in recent weeks, a flurry of MiG fighter jet activity in Belarusian airspace has prompted a number of air raid alarms throughout Ukraine.