Russia's military campaign in Ukraine appears to be faltering as its forces struggle to take more territory in the Donbas amid fierce resistance, Western military officials said.
After initially failing to take the capital, Kyiv, in the first weeks of the war, Russian forces have refocused their efforts on eastern and southern Ukraine.
However, their offensives have been met with substantial resistance, with some Western intelligence saying Russia may have lost up to one-third of its combat strength since it began its unprovoked invasion on February 24.
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"The brutal invasion [by] Russia is losing momentum," NATO Deputy-Secretary General Mircea Geoana said on May 15. "We know that with the bravery of the Ukrainian people and army, and with our help, Ukraine can win this war."
Geoana made the comments in Berlin, where top NATO diplomats gathered to discuss providing further support to Ukraine and moves by Finland, Sweden, and others to join the Western alliance in the face of threats from Russia.
Geoana, who chaired the meeting, said Ukraine's supporters were "united, we are strong, will continue to help Ukraine in winning this war."
Alliance members have already given the country billions of dollars in lethal and nonlethal military aid to help repel the largest invasion in Europe since the end of World War II.
According to Ukrainian Foreign Minister Dmytro Kuleba, "more weapons and other aid" was "on the way to Ukraine."
The United States and other NATO members have given Ukraine anti-tank and anti-aircraft weapons, as well as well as heavy artillery.
Kuleba made the comment after meeting U.S. Secretary of State Antony Blinken in Berlin. State Department spokesman Ned Price said Blinken conveyed details regarding the latest tranche of U.S. security assistance to bolster Ukraine's defenses.
Kuleba was due to brief NATO foreign ministers on the situation on the ground in Ukraine and on how the alliance can further help the country as it battles invading Russian forces for a 12th week.
U.S. Senate Republican Leader Mitch McConnell, in Stockholm after visiting the Ukrainian capital on May 14, told reporters on a conference call that he expected the Senate to approve just under $40 billion in further aid for Ukraine in a vote on May 18.
U.S. President Joe Biden had requested $33 billion in aid for Ukraine on April 28, including over $20 billion in military assistance. But House lawmakers boosted that amount to roughly $40 billion, adding more military and humanitarian aid.
British military intelligence said in its regular update that the Russian forces' offensive in Ukraine's eastern Donbas region "has lost momentum and fallen significantly behind schedule."
Russia has now likely suffered losses of one-third of the ground combat force it committed in February, Britain's Ministry of Defense tweeted on May 15.
Many of those losses occurred in the first few weeks of the war as Russia sought to capture Kyiv and impose a puppet regime loyal to Moscow. Russia has since shifted its focus to the Donbas, an area comprising the Luhansk and Donetsk regions.
Britain's Defense Ministry said that despite small-scale initial advances, Russia has failed to achieve substantial territorial gains in the Donbas over the past month while sustaining consistently high levels of attrition.
Russian forces are increasingly constrained by degraded enabling capabilities, continued low morale, and reduced combat effectiveness, the ministry said.
"Many of these capabilities cannot be quickly replaced or reconstituted, and are likely to continue to hinder Russian operations in Ukraine," the bulletin added.
The ministry predicts that under the current conditions, Russia is unlikely to dramatically accelerate its rate of advance over the next 30 days.
The assessments of Russia's war performance came as Russian troops retreated from around Kharkiv, Ukraine's second-largest city, after bombarding it for weeks.
The largely Russian-speaking city with a prewar population of 1.4 million was a key military objective earlier in the war, when Russia hoped to capture and hold major Ukrainian cities.
Ukraine's military says that Moscow is now focusing on guarding supply routes, while launching mortar, artillery, and air strikes in eastern Ukraine in an attempt to deplete Ukrainian forces and destroy fortifications.
Ukrainian President Volodymyr Zelenskiy said in his nightly address early on May 15 that "the situation in Donbas remains very difficult" and Russian troops were "still trying to come out at least somewhat victorious."
Russian forces continued attacks on May 15, shelling military infrastructure in the Lviv region in western Ukraine. No deaths or casualties were reported following the rocket attack, Lviv Governor Maksym Kozytskiy said on Telegram.
The governor said the extent of the destruction was being investigated. One site near Yavoriv -- presumably around the military training area there -- was "completely destroyed," according to the governor.
Earlier, a regional air command of Ukraine said several missiles had been fired at the Lviv region from the Black Sea in the early hours of May 15.
This was the first Russian air strike in about a week in the region near the Polish border.
With reporting by AP, Reuters, and dpa