The United States will host an expected gathering of more than 40 countries on Tuesday for Ukraine-related defense talks that will focus on arming Kyiv so it can defend against an unfolding and potentially decisive Russian onslaught in the east, U.S. officials said.

U.S. Defense Secretary Lloyd Austin is holding the event at Ramstein Air Base in Germany following a trip to Kyiv where he pledged additional support to Ukrainian President Volodymyr Zelenskiy's war effort.

U.S. Army General Mark Milley, chairman of the Joint Chiefs of Staff, said a key goal of the talks was to synchronize and coordinate mounting security assistance to Kyiv that includes heavy weaponry, like howitzer artillery, as well armed drones and ammunition.

"The next several weeks will be very, very critical," Milley told reporters traveling with him. "They need continued support in order to be successful on the battlefield. And that's really the purpose of this conference."

Driven back by Ukrainian forces from a failed assault on Kyiv in the north, Moscow has redeployed its troops into the east for a ground offensive in two provinces known as the Donbas.

U.S. officials, speaking on condition of anonymity, assess that Russia will rely heavily on artillery strikes, trying to pound Ukrainian positions as Moscow moves in ground forces from multiple directions to try to envelop and wipe out a significant chunk of Ukraine's military.

But the United States also estimates many Russian units are depleted, with some operating with personnel losses as high as 30% -- a level considered by the U.S. military to be too high to keep fighting, officials say.

U.S. officials cite anecdotes like Russian tanks with sole drivers and no crew and substandard equipment that is either prone to breakdowns or out of date.

British assessments showed that around 15,000 Russian personnel had been killed in the conflict while 2,000 armored vehicles including some 530 tanks had been destroyed, along with 60 helicopters and fighter jets, Defence Secretary Ben Wallace said on Monday.

Russia has so far acknowledged only 1,351 troops killed and 3,825 wounded.

Russia still has advanced capabilities and superior force numbers, and has shown a willingness to keep pouring soldiers and units into the fight, U.S. officials said.

Moscow can also economically afford to wage a long war in Ukraine despite being hammered by Western sanctions, defense experts and economists said.

For its part, Ukraine boasts high morale, creative and adaptive battlefield tactics and local knowledge of the terrain, along with arms and intelligence from the United States and its allies.

"They definitely stand a fighting chance," a U.S. military official said, speaking on condition of anonymity.

Speaking to reporters after his trip to Ukraine, Austin said: "They can win if they have the right equipment, the right support."

The meeting, which aims to ensure a steady flow of such aid, is taking place at Ramstein, a sprawling air base southwest of Frankfurt which only months ago was grappling with an influx of Afghan evacuees after the Taliban takeover of that country last summer.

Russia's Feb. 24 invasion of Ukraine has killed thousands of people, displaced millions more and raised fears of a wider confrontation between Russia and the United States - by far the world's two biggest nuclear powers.

Putin says the "special military operation" in Ukraine is necessary because the United States was using Ukraine to threaten Russia and Ukraine was guilty of the genocide of Russian-speaking people.

Ukraine says it is fighting a land grab by Russia and that Putin's accusations of genocide are nonsense.