KYIV, UKRAINE -- Ukraine's troops have been forced to make a tactical retreat from three villages in the embattled east, the country's army chief said Sunday, warning of a worsening battlefield situation as Ukrainian forces wait for much-needed arms from a huge U.S. aid package to reach combat zones.

Col. Gen. Oleksandr Syrskyi reported that Russian forces continue to attack 鈥渁long the entire front line鈥 of more than 1,000 kilometres (620 miles), with pitched battles raging west of Avdiivka, the eastern city they took in February after a grueling, monthslong fight.

鈥淭he most difficult situation is in the Pokrovsk and Kurakhove directions, where fierce battles continue," Syrskyi's said in an update posted to the Telegram messaging app, referencing two Ukrainian-held cities in the war-torn Donetsk region, once a hub of industry.

鈥淭he enemy has engaged up to four brigades in these directions, is trying to develop an offensive west of Avdiivka and Marinka, making its way to Pokrovsk and Kurakhove,鈥 Syrskyi added. "Units of the Defense Forces of Ukraine, preserving the lives and health of our defenders, moved to new frontiers west of Berdychi, Semenivka and Novomykhailivka."

Two of these front-line villages lie less than 50 kilometres (31 miles) east of Pokrovsk, while the third is located just over 30 kilometres (19 miles) by road from Kurakhove.

A Washington-based think tank predicted late Saturday that Russian forces 鈥渨ill likely make significant tactical gains in the coming weeks," as acute ammunition shortages continue to hobble Ukraine's defense efforts.

In its latest operational assessment, the Institute for the Study of War said that Moscow鈥檚 forces have opportunities to push forward around Avdiivka, and also threaten nearby Chasiv Yar. Its capture would give Russia control of a hilltop from which it can attack other key cities forming the backbone of Ukraine鈥檚 eastern defenses.

Despite this, the think tank assessed that neither of these efforts by Moscow are likely to cause Kyiv鈥檚 defensive lines to collapse 鈥渋n the near term.鈥

The Russian Defense Ministry on Sunday confirmed that Moscow鈥檚 troops had taken a village about 15 kilometres (nine miles) north of Avdiivka, days after the war institute reported on its likely capture early on Thursday. That day鈥檚 assessment described Moscow鈥檚 gains as 鈥渞elatively quick but still relatively marginal,鈥 adding that Russian troops had advanced by no more than five kilometres (three miles) over the previous week.

U.S. President Joe Biden promised on Wednesday that U.S. weapons shipments would begin making their way into Ukraine within hours, as he signed into law a US$95 billion measure 鈥 US$61 billion of which was allocated for Ukraine 鈥 that also included assistance for Israel, Taiwan and other global hot spots. The announcement marked an end to the long, painful battle with Republicans in Congress over urgently needed assistance for Ukraine.

Elsewhere, Russian drones struck the Ukrainian Black Sea city of Mykolaiv early Sunday, setting a hotel ablaze and damaging infrastructure, according to local officials.

Vitaliy Kim, the governor of Ukraine鈥檚 southern Mykolaiv province, said that the drones 鈥渟eriously damaged鈥 a hotel in its namesake capital, sparking a fire that was later extinguished. Kim also reported that the strike damaged heat-generating infrastructure in the city. He added that there were no casualties.

Russian state agency RIA reported that the strike on Mykolaiv targeted a shipyard where naval drones are assembled, as well as a hotel housing 鈥淓nglish-speaking mercenaries鈥 who have fought for Kyiv. The RIA report cited Sergei Lebedev, described as a coordinator of local pro-Moscow guerrillas. His comments couldn't be independently verified.

Also on Sunday morning, the Russian Defense Ministry said that 17 Ukrainian drones were downed overnight over four regions in the country鈥檚 southwest. Three drones were intercepted near an oil depot in Lyudinovo, an industrial town about 230 kilometres (143 miles) north of the Ukrainian border, Gov. Vladislav Shapsha said.

One of the Ukrainian drones damaged communications infrastructure in Russia's southern Belgorod province, which borders Ukraine, Gov. Vyachaslav Gladkov said later on Sunday. There were no immediate reports of casualties.

The Russian Defense Ministry claimed Sunday that its forces had destroyed ammunition depots and military equipment housed at three airports across Ukraine, including assault drones stored at Kamyanka Airfield in the country's east. The ministry's online update said the attacks took place over the last 24 hours. There was no immediate comment from Kyiv.

Russian shelling on Saturday and overnight wounded at least seven civilians across Ukraine, according to Ukrainian officials. A 36-year-old woman was pulled alive from the rubble after Russian shells on Sunday morning destroyed her home in the northeastern Kharkiv region, the local administration reported. Her 52-year-old neighbor was also rushed to a hospital with a stomach wound, the administration said.