Ukraine's troops are "gaining ground" as they begin a long-anticipated counteroffensive that seeks to end Russia's occupation of Ukrainian territories, Stoltenberg said alongside Secretary of State Antony Blinken at the State Department.
"Ukraine is making a difference on the battlefield as we speak, because the Ukrainians have launched the offensive. They are making advances. They are gaining ground," he said.
Stoltenberg emphasized that the push is still in its "early days," but the more territory Kyiv is able to wrest from Moscow's control "the stronger their hand will be at the negotiating table, and the more likely it is that President Putin will understand that we will never win this battle, he will never win the war of aggression on the battlefield. "
Earlier Tuesday, Ukraine said its forces made advances on the front line with Russia in the regions of Donetsk and Zaporizhzhia amid "counteroffensive actions" announced by President Volodymyr Zelenskyy during the weekend.
"In the course of the offensive operation, during the past day, our troops advanced 250 meters (820 feet) in the direction of Bakhmut in the area of the Berkhiv Reservoir and 200 meters (656 feet) in the Toretsk direction," Deputy Defense Minister Hanna Maliar said in a statement on Telegram.
Maliar further asserted advances in the Zaporizhzhia region near Berdiansk. The claims could not be immediately verified.
She added that Ukrainian forces have been encountering minefields and anti-tank ditches, as well as "constant counterattacks by enemy units on armored vehicles and the massive use of ATGMs (anti-tank guided missiles) and kamikaze drones" during the counteroffensive.
Blinken said he expects a new "robust package" of political and military aid for Ukraine will be announced when NATO leaders convene in Vilnius, Lithuania next month.
