The US think tank warned Moscow's army plans to mount a sweeping offensive as weather conditions on the front improve.
ADVERTISEMENTThe Institute for the Study of War (ISW) has said Russia may be preparing a new offensive in Ukraine in the coming weeks.
The US-based think tank's announcement comes amid concerns that newly approved arms supplies from Washington will not reach Kyiv in time.
Delays in Western assistance have already helped Russia make incremental gains along the frontline.
"Ukrainian forces currently are under immense constraints due to material shortages and delays in Western security assistance," explained ISW Russia analyst Riley Baily.
"Ukrainian forces do not have the capabilities that they previously had to blunt a lot of the Russian advance."
"Russian forces are gradually restoring, manoeuvring in the battlefield and threaten to make operationally significant advances this summer during an expected large-scale Russian offensive operation," he added.
The ISW says Russia appears to be planning fresh assaults on key locations, including the strategically important town of Chasiv Yar.
"If Russian forces seize Chasiv Yar, they then have a position from which they could launch subsequent offensive operations on to Konstantikovkivka and Kruskivka," explained Baily.
"These are major cities and then oblast that form the backbone of Ukrainian defence. And that would be very significant."
Long-awaited events
Kyiv has also been warning of a Russian spring offensive for some time.
Its capacity to repel any such attempted advance largely depends on receiving Western military supplies as soon as possible, say analysts.
Ukrainian and Western leaders on Sunday welcomed a desperately needed aid package passed by the US House of Representatives.
The bulk of the funding will go to Ukraine, with other countries like Israel and Taiwan benefitting as well.
Ukrainian President Volodymyr Zelenskyy, who had warned that his country would lose the war without US funding, said the aid is urgently needed on the frontline.