Against the background of US warnings of a possible invasion of Russian troops on February 16, Ukrainian President Volodymyr Zelenskyj declared the date by decree as Unity Day.
"We are told that February 16 will be the day of the raid, we will make it Unity Day," the head of state said in a video on Monday evening.
Ukrainians are scheduled to hoist flags across the country this Wednesday and sing the anthem at 10:00 a.m. local time (9:00 a.m. CET).
"Let's show our unity to the whole world," said the 44-year-old.
In his speech, Zelenskyi again denied Russian accusations that it was preparing for an offensive against the breakaway Luhansk and Donetsk regions in eastern Ukraine.
"Donbass and Crimea will only return to Ukraine through diplomatic channels," the president said.
Russia annexed the Black Sea Peninsula in 2014 and then also supported the Moscow-friendly separatists in eastern Ukraine.
The United States in particular has been warning of a Russian invasion of Ukraine for weeks.
To this end, tens of thousands of Russian soldiers were gathered not far from the Ukrainian border.
The Kremlin regularly denies the allegations.
According to its own statements, Kiev also has no such information about an approaching raid.
Since then, government troops have been fighting Russian-backed separatists in the eastern Ukrainian region of Donbass.
According to UN estimates, more than 14,000 people have already been killed.