The weather service, which has kept records since 1881, is forecasting temperatures above 35 degrees Celsius (95 degrees Fahrenheit) on Thursday and Friday.
The government coronavirus task force said that 339 people had died of coronavirus-related causes in the last 24 hours. That pushed the death toll to 121,501.
Navalny's probe into a Black Sea palace Russian tycoons allegedly built for Putin has racked up more than 116 million views on YouTube since its release in January. Putin denies the palace is his.