WASHINGTON (NewsNation) — The U.S. is set to finalize a huge military aid package for Ukraine totaling as much as $2.6 billion worth of weaponry.

However, a senior official at the Pentagon, who recently returned from meeting Ukrainian President Volodymyr Zelenskyy, told NewsNation that the U.S. is “not there yet” on sending Ukraine the Abrams tanks it’s so desperately requesting.

A defense official told NewsNation that the U.S. doesn’t want to send these complicated, powerful and pricey tanks to Ukrainians who might not be able to maintain them.

This does not mean that the U.S. isn’t going to send more resources to Ukraine. The new package is expected to include for the first time nearly 100 Stryker combat vehicles and at least 50 Bradley armored vehicles to allow Ukrainian forces to move more quickly and securely on the front lines in the war with Russia.

The officials said the numbers could change as the Biden administration goes through final deliberations on the package. An announcement is expected this week, when defense leaders from the U.S., Europe and other regions gather in Germany to discuss military support for Ukraine. The aid is also expected to include thousands of rounds of ammunition, including rockets for air defense systems.

The officials spoke on condition of anonymity because the aid has not yet been made public.

The decision to send the Strykers, which could be delivered within weeks, comes on the heels of announcements by the British to send Ukraine battle tanks, which have long been sought by Ukrainian leaders.

Under Secretary of Defense for Policy Colin Kahl told reporters Wednesday that a new phase of the war is shaping up as Russia gets more deeply entrenched, and that Ukraine will need mechanized infantry to break through those lines.

Speaking at the World Economic Forum’s annual meeting in Davos, Switzerland, on Thursday, Zelenskyy bared his frustration about not obtaining enough tanks from some Western countries to help Ukraine’s defend against Russian forces.

Speaking by video link at a breakfast with U.S. Sen. Chris Coons, Dutch Prime Minister Mark Rutte and former British Prime Minister Boris Johnson, Zelenskyy offered a veiled critique of countries like Germany, Poland and the United States — crucial supporters of Ukraine — that have nonetheless hesitated about sending tanks.

Zelenskyy bemoaned a “lack of specific weaponry” and said that to win the war, “We cannot just do it with motivation and morale.”

“And I would like to thank again for the assistance from our partners,” he said at the Victor Pinchuk Foundation breakfast through an interpreter. “But at the same time, there are times where we shouldn’t hesitate or we shouldn’t compare when someone says, ‘I will give tanks if someone else will also share his tanks.’”

Zelenskyy also said air defense was “our weakness” in light of targeted Russian strikes, including use of Iranian-made drones, and reiterated his call for supplies of long-range artillery to fire at Russian forces in Ukrainian territory — not fire into Russia itself.

The U.S. has led the world in supplying aid to Ukraine in its fight against Russia. For months, Ukraine has sought to be supplied with heavier tanks, including the U.S. Abrams and the German-made Leopard 2 tanks, but Western leaders have been treading carefully.

The Associated Press contributed to this report.