Ukrainian forces likely used “tactical surprise” to advance at least 12 miles into Russian-held territory in the Kharkiv region on Wednesday.

The U.S. and its allies estimate that tens of thousands of Russian troops have been killed or wounded and huge amounts of military equipment destroyed since Putin ordered the Feb. 24 invasion.

Shelling continued around Europe’s largest nuclear plant on Tuesday, a day after it was again knocked off Ukraine’s electrical grid and put in the precarious position of relying on its own power to run its safety systems.

Six of the international agency’s experts remain at the plant, and there will be a ‘permanent presence on site … with two of our experts who will be continuing the work.’

The U.S. government highlighted its finding as Russian President Vladimir Putin last week ordered the Russian military to increase the number of troops by 137,000 to a total of 1.15 million.