Ukraine is at a pivotal moment on the battlefield, U.S. Secretary of Defense Lloyd Austin has said.

"The stakes are too high. Ukraine is at a decisive moment on the battlefield. And we are seeing what President [of Ukraine Volodymyr] Zelensky warned us about. After failing to capture Kyiv and reassessing its combat goals, Russia has shifted its focus to the Donbas. And we cannot underestimate the challenge Ukraine is facing," he said at the opening of a meeting of the Contact Group on Ukraine's Defense in Brussels on Wednesday.

Austin stressed that he was personally grateful for the significant security assistance provided to Ukraine by the contact group.

"But we can't afford to give up and slow down," he added.