Ukraine has dealt a powerful blow to invading Russian forces.

Last week, the Ukrainian military launched a surprise counterattack against the Russian forces invading from the northeastern border, primarily around the Kharkiv region. This powerful counterattack has sent the Russian forces reeling, with Ukrainian soldiers reporting that the Russian chain of command has been severely disrupted as their soldiers beat a hasty retreat. The attacks follow an effort from Russia last week to deploy troops to the southern front, a opportunity military strategists believe Ukraine deliberately exploited to push them back.

“In the face of Ukrainian advances, Russia has likely ordered the withdrawal of its troops from the entirety of occupied Kharkiv Oblast west of the Oskil River,” the U.K.’s Ministry of Defense said on Twitter, adding that since the counterattacks began last week, “Ukraine has recaptured territory at least twice the size of Greater London.”

″Ukrainian forces have reportedly attacked and made gains at several important locations on the western bank of the Dnipro River,” the Institute for the Study of War said Sunday. “Ukraine has committed considerable combat power and focused a significant portion of the Western-supplied long-range precision systems it has to this axis, and it is not likely to have done so merely to draw Russian forces to the area.”

Strategists have proclaimed this fierce offensive to be a major loss for Russia, and a major win for Ukraine. “It really seems like the Russian forces have exhausted themselves in terms of their ability to to make advances. They haven’t really gained any territory to speak of since since that last push in Luhansk in late June, early July,” said Dmitry Gorenburg, senior research scientist at the security research and analysis organization CNA.