(LONDON) — Ukrainian President Volodymyr Zelenskyy acknowledged for the first time that his country’s military is conducting a cross-border offensive inside Russia.

The Ukrainian military was progressing in its campaign “to push the war out into the aggressor’s territory,” Zelenskyy said late Saturday in his nightly address.

“Ukraine is proving that it really knows how to restore justice and guarantees exactly the kind of pressure that is needed — pressure on the aggressor,” he added.

Ukraine’s attack began last week and appeared to be a large-scale offensive operation, involving at least two Ukrainian brigades.

Ukrainian troops in the first days appeared to have captured a number of settlements in the Kursk border area while advancing, reaching perhaps as far as about 9 miles inside Russia by Wednesday. A blog closely linked to Russia’s defense ministry reported Thursday that Ukrainian armored units were seen about 18.5 miles inside Russia’s border.

Zelenskyy on Saturday thanked “every unit of our Defense Forces that makes this happen.”

The Russian Defence Ministry has in statements claimed Ukrainian forces were taking heavy casualties.

The Ukrainian military lost more thank 1,100 service members and more than 100 armoured vehicles, including 22 tanks, since the incursion began, Russia claimed. Ten of those tanks had been destroyed in just 24 hours of fighting, the ministry said in a statement on Saturday.

More Russian conscripts were moved into the region in the recent days, including some who had been redeployed from frontline positions elsewhere, according to the Institute for the Study of War, a nonprofit think tank in Washington.

“Russian forces appear to be more adequately defending against Ukrainian assaults following the arrival of additional conscripts and more combat effective personnel from frontline areas in Ukraine,” the think tank said Saturday.

ABC News’ Patrick Reevell and Kevin Shalvey contributed to this report.

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