Temperatures in the Arctic Circle are likely to have hit an all-time record on Saturday, reaching a scorching 38C (100F) in Verkhoyansk, a Siberian town.
The record still needs to be verified, but it appears to have been 18C higher than the average maximum daily temperature in June.
Hot summer weather is not uncommon in the Arctic Circle, but recent months have seen abnormally high temperatures.
The Arctic is believed to be warming twice as fast as the global average.
Verkhoyansk, home to about 1,300 people, sits just inside the Arctic Circle, in remote Siberia. It has an extreme climate with temperatures plunging in January to an average maximum of -42C and then surging in June to 20C.
But a persistent heatwave this year in the Arctic Circle has worried meteorologists. In March, April and May, the Copernicus Climate Change service reported that the average temperature was around 10C above normal.