WATCH: White House press secretary Karine Jean-Pierre says Ukraine using U.S. weapons ‘with great effect’

As Ukrainian troops apply pressure on retreating Russian forces, pressing a counteroffensive that has produced a stunning blow to Moscow’s military prestige, the White House says Ukraine is using advanced rocket systems provided by the U.S. “with great effect.”

Watch the briefing in the player above.

“Clearly, at least in the Donbas, there’s a sense of momentum here by the Ukrainian armed forces,” said National Security Council spokesman John Kirby.

“I won’t get ahead of future security assistance packages,” Kirby said. “I do think you’ll see another one here in coming days,” he said. “We’re in lockstep with the Ukrainians, talking to them every day.”

As the advance continued, Ukraine’s border guard services said the army took control of Vovchansk — a town just 3 kilometers (2 miles) from Russia seized on the first day of the war. Russia acknowledged that it has withdrawn troops from areas in the northeastern region of Kharkiv in recent days.

It was not yet clear if the Ukrainian blitz, which unfolded after months of little discernible movement, could signal a turning point in the nearly seven-month war.

READ MORE: Ukraine continues to pressure retreating Russian troops

“I would let President Zelenskyy determine and decide whether he feels militarily they’ve reached a turning point,” Kirby said.

Ukrainian officials have been buoyant, releasing footage showing their forces burning Russian flags and inspecting abandoned, charred tanks. In one video, border guards tore down a poster that read, “We are one people with Russia.”

Momentum has switched back and forth before, and Ukraine’s American allies were careful not to declare a premature victory since Russian President Vladimir Putin still has troops and resources to tap.

“Mr. Putin still has an awful lot of military capacity left at his disposal, not just to be used in Ukraine, but but potentially elsewhere,” Kirby said.

Late Monday, President Volodymyr Zelenskyy said his troops had so far retaken more than 6,000 square kilometers (2,300 square miles) — an area more than twice the size of Luxembourg — in a matter of weeks.

The counteroffensive has provoked rare public criticism inside Russia of Putin’s war. Meanwhile, some of its defenders in Russia played down the idea that the success belonged to Ukraine, blaming instead Western weapons and fighters for the losses.