WASHINGTON (NEXSTAR) — Western allies continue to promise more support, including weapons, to Ukraine, though Germany has so far held off on approving sending battle tanks there.

Ukraine’s president has argued the tanks are necessary to defeat Russia, which invaded the nation 11 months ago.

“Time remains a Russian weapon. … We have to speed up,” President Volodymyr Zelenskyy said in a virtual call Friday. “Hundreds of thank yous are not hundreds of tanks.”

Poland said it’s ready to send Leopard tanks to its neighbor Ukraine, but Germany, which made the tanks, is blocking the move over concerns that Russia would use it as an excuse to retaliate.

White House spokesman John Kirby on Friday supported Germany’s stance and the U.S. objection to sending additional tanks of its own.

“We are not arm twisting,” Kirby said of negotiations with Germany.

He added that tanks are “very expensive to operate, very expensive to fuel, very expensive to maintain” and require a lot of training to operate.

The Biden administration says the latest $2.5 billion U.S. aid package to Ukraine will help. Kirby said it includes “more than 500 armored vehicles, including Bradleys, Stryker combat vehicles, mine-resistant ambush protected vehicles.”

“What we’ve said is we’re going to continue to help them defend themselves, defend their sovereignty, win back their territory as they should, as they must,” Kirby said.

Pressure is mounting for Germany to change its position. After a Friday meeting, the German defense minister said it will make a decision as soon as possible.