Ukraine's military says heavy fighting continues in eastern and southern regions of the country.

It says on Saturday Russian forces carried out more than 30 attacks near Avdiivka, a strategically important city in the eastern region of Donetsk.

And it says Russian air strikes in various parts of the country resulted in civilian injuries.

Sunday marks 22 months since the start of the full-fledged Russian invasion.

Russian and Ukrainian forces are said to be in a stalemate following a major counteroffensive by Ukraine in June this year.

Ukrainian forces are struggling to maintain a sufficient number of soldiers as the conflict drags on and concerns deepen about a shortage of ammunition as the future of aid from the United States remains uncertain.

President Volodymyr Zelenskyy revealed Friday that preparations have begun for the delivery of F-16 fighter jets from the Netherlands.

The UK Ministry of Defense said in a social media post on Saturday that "both Ukrainian and Russian troops have highly likely suffered from exceptional levels of rats and mice infestation in some sectors of the front line."

It added that the rodents "are likely seeking shelter in vehicles and defensive positions. Rodents will add further pressure to front line combatants' morale."