Ukrainian President Volodymyr Zelenskyy has appealed for national unity on the anniversary of the 1991 referendum that confirmed overwhelming support for independence from the former Soviet Union.

In a video message on Thursday, Zelenskyy said that every year on December 1, Ukrainians recall an event that defined history.

Zelenskyy added that Ukrainians' desire to live freely will not be broken and they "will never again be gears of some empires."

The Ukrainian military is on high alert against fresh missile attacks by Russia that target infrastructure facilities.

A senior Ukrainian military official said on Thursday that "there is still a threat of the enemy launching missile strikes" on critical infrastructure throughout Ukraine in the near future.

Russia is repeatedly launching massive missile attacks across Ukraine, causing serious power shortages in the severe cold weather.

Over nine months into Russia's military invasion, Ukraine faces the challenge of providing psychological care for soldiers and their families.

A publically-run facility in Lviv in western Ukraine says it has helped about 1,000 traumatized soldiers since the start of the invasion.

The center says soldiers are suffering from flashbacks of their experiences on the battlefield and some have become dependent on alcohol and drugs. It says the number of soldiers and family members who need help is increasing.

The head of the center says they hope to continue offering necessary support to soldiers and their families.