Ukrainian President Volodymyr Zelensky has accused Russia of using “nuclear blackmail” at the Zaporizhzhia nuclear power plant – Europe’s largest.
Russia seized the plant in March and has been accused of turning it into a base from where it hits nearby towns.
Both countries have traded blame for shelling it in recent days, prompting UN warnings of a nuclear disaster.
Mr Zelensky says any Russian soldier who shoots at or under the cover of the plant will be a “special target”.
The six-nuclear reactor Zaporizhzhia station is located in the city of Enerhodar, on the eastern bank of the Dnieper River (Dnipro in Ukrainian) in southern Ukraine.
Russia invaded Ukraine on 24 February, seizing the plant within days. Moscow has kept Ukrainian personnel to operate the facility.
The UN has warned that continued hostilities around the station could lead to a nuclear disaster affecting much of Europe.
Russia has repeatedly denied any wrongdoing at the plant.
It says it seized control of the plant to prevent leaks of radioactive materials during fighting in the region.
During his video address late on Saturday, Mr Zelensky said Russia had engaged in “constant provocations” by firing on the plant and said forces stationed there had used it as a base to shell the cities of Nikopol and Marhanets – on the other bank of the river.
This was being done, the president said, to “blackmail our state and the entire free world”. But he stressed that “Russian blackmail only mobilises even more global efforts to confront terror”.
“Every Russian soldier who either shoots at the plant, or shoots under the cover of the plant, must understand that he is becoming a special target for our intelligence, for our special services, for our army,” the president said.
He added that “every day” of Russia’s occupation of the plant “increases the radiation threat to Europe”.
Ukraine’s defence intelligence agency also accused Russia of a provocation by parking a Pion self-propelled heavy artillery piece outside a nearby town and painting a Ukrainian flag on it, in an attempt to discredit Kyiv.
A BBC investigation revealed earlier this week that many of the Ukrainian workers at the site are being kept under armed guard amid harsh conditions.
On Thursday, foreign ministers from the G7 group of industrial democracies demanded that Russia withdraw from the site immediately.
Their warning echoed statements from the United Nations’ nuclear watchdog, the International Atomic Energy Agency (IAEA), which called for an end to “all military activities that endanger nuclear security”.
UN Secretary General António Guterres has warned that the situation at the plant could “lead to disaster”.