Ukrainian President Volodymyr Zelenskiy says Ukrainian forces in the eastern city of Soledar are holding their positions and inflicting significant losses on Russia troops.
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The Ukrainian troops defending the two cities will receive "ammunition and everything necessary promptly and without interruption," Zelenskiy said on Telegram on January 12 after a meeting of Ukraine's top military leaders.
Zelenskiy said the meeting also addressed the reinforcement of Ukraine's armed forces with equipment and weapons supplied by partners.
Ukraine's military said earlier that the assault on the salt-mining town of Soledar was continuing, despite earlier Russian claims that the city had been captured.
Russian forces overnight used artillery, rockets, and aircraft to pummel the city, which is a northeastern suburb of the strategic city of Bakhmut, which could be vulnerable to capture if Soledar is taken.
"The fiercest and heaviest fighting is continuing today in the area of Soledar," Ukrainian Deputy Defense Minister Hanna Malyar said on January 12.
"Despite the difficult situation, Ukrainian soldiers are fighting doggedly," she added.
Satellite imagery of Soledar released by Maxar Technologies on January 11 showed a city devastated by weeks of intense fighting.
Russia-installed occupation officials in Ukraine’s Donetsk region said that "pockets of resistance" remain within the city, while a Russian Defense Ministry official in Moscow claimed the offensive in the Donetsk region was proceeding "successfully."
Earlier, the Kremlin-connected businessman Yevgeny Prigozhin, who heads the ostensibly private Russian mercenary group Vagner, said his forces had captured the city.
The Kremlin, however, urged caution, saying that while there had been a "positive dynamic in advances," there should be no rush to declare victory and instead wait for "official information" on the situation.
RFE/RL could not independently verify any of the assertions.
Also during the night, the Russian military reportedly shelled the southern city of Zaporizhzhya, local Ukrainian officials reported.
The shelling, shortly after 3 a.m. local time, damaged some infrastructure but no casualties were reported, city council official Anatoliy Kurtev said.
Salt Of The Earth: Deep Inside Eastern Ukraine's Massive Soledar Mines
Ukraine’s electricity provider, Ukrenerho, reported blackouts in nine regions across the country on January 12.
Since October, Russia has been carrying out air strikes across Ukraine targeting the electrical grid and other civilian infrastructure and causing disruptions in electricity, water, and heat supplies.
On January 11, Moscow announced a reorganization of its military command, placing Chief of the General Staff Valery Gerasimov in charge of the war in Ukraine, which the Kremlin calls a "special military operation." Gerasimov replaces General Sergei Surovikin, who was named Gerasimov's deputy. Surovikin was made overall commander of the war just three months ago.
A Pentagon spokesman on January 12 said Russia's persistent troubles in Ukraine likely led to the shake-up.
"It likely does reflect some of the systemic challenges that the Russian military has faced since the beginning of this invasion," Brigadier General Patrick Ryder told a news briefing.
Among the issues are logistics problems, command-and-control problems, sustainment problems, morale, and the "failure to achieve the strategic objectives that they've set for themselves," Ryder said.
He urged Moscow to end the war instead of turning to new generals to oversee the invasion.
In an assessment issued on January 11, the U.S.-based Institute for the Study of War claimed Russia is suffering from "munitions shortages" that "hinder the ability of Russian forces to sustain offensive operations."
"Russian sources are increasingly…acknowledging that Russia's ammunition and supply shortages are decisively impeding the ability of Russian forces to advance," the assessment stated.
In Moscow, a deputy in the State Duma -- the lower house of Russia’s parliament -- said lawmakers planned to raise the upper age for the military draft to 30 years old in order to boost the number of Russian troops by 30 percent.
Andrei Kartapolov, chairman of the Duma's Defense Committee, said the lower age limit, which currently stands at 18, would be raised to 21 after a "transition period" of one to three years.
Kremlin spokesman Dmitry Peskov said President Vladimir Putin "conceptually supported" the idea of raising the draft age.