KYIV — President Zelensky met with Ukraine’s top general on Thursday and told him it’s time for someone new to lead the army in what amounts to a major shake-up of Ukraine’s war strategy.

In a post on X, Mr. Zelensky said he thanked General Valerii Zaluzhnyi for his two years of service as commander-in-chief and discussed possible replacements for the top military job. “The time for such a renewal is now,” Mr. Zelensky said.

Mr. Zelenskyy says he has appointed Сolonel General Oleksandr Syrskyi, the commander of Ukraine’s ground forces, to lead the army. General Syrskyi, 58, has since 2013 been involved in the Ukrainian army’s effort to adopt NATO standards.

General Zaluzhnyi, in a Telegram message, did not announce he had stepped down but said he accepted that “everyone must change and adapt to new realities” and agreed that there is a “need to change approaches and strategy” in the war.

The statement followed days of speculation spurred by local media reports that Mr. Zelenskyy would sack General Zaluzhnyi, a move that would amount to the most serious shakeup of the top military brass since Russia’s full-scale invasion of Ukraine.

Meanwhile, Ukrainian forces claimed to have shot down a Russian attack helicopter in eastern Ukraine near the city of Avdiivka, where soldiers are fighting from street to street as Russia’s army steps up its four-month campaign to surround Kyiv’s defending troops.

Ukrainian soldiers used a portable anti-aircraft missile to take down the Ka-52 Alligator attack helicopter, one of the Russian air force’s deadliest weapons, according to the commander of Ukrainian units fighting on the southeastern front line, Oleksandr Tarnavskyi.

The roughly 930-mile line of contact has shifted little during recent months of wintry weather. As the war in Ukraine nears its two-year anniversary, though, Avdiivka has become “a primary focus” of Moscow’s forces, Britain’s defense ministry said in an assessment Thursday.

Street-to-street combat is taking place in the city as Ukrainian troops seek to keep open their main supply route amid intense bombardment, the ministry said on X, formerly known as Twitter.

The General Staff of Ukraine’s armed forces reported Thursday that its troops had fended off 40 enemy assaults around Avdiivka over the previous 24 hours. That is roughly double the number of daily Russian assaults at other points along the front line.

Russia’s Pravda newspaper reported Thursday that the Russian army was attempting to cut a key logistics supply route for Ukraine in the village of Lastochkyne, about 4 miles west of Avdiivka.

The Russian military has used electronic warfare to take out the Starlink communications system which Ukrainian troops use to communicate, Pravda said.

Ukraine has built multiple defenses at Avdiivka, complete with concrete fortifications and a network of tunnels. Despite substantial losses of personnel and equipment, Russian troops have slowly advanced since October.

The fight has evolved into a gruesome effort for both sides. It has been compared to the nine months of fighting for Bakhmut, the Ukraine war’s longest and bloodiest battle. It ended with Russia capturing the bombed-out, deserted city last May in what Moscow hailed as a major triumph.

Both Bakhmut and Avdiivka are located in Ukraine’s Donetsk region. Moscow-backed rebels seized part of the region in 2014 and Russia illegally annexed all of it in 2022 with three other Ukrainian regions.

Russia wants to capture the entire Donetsk region, where it currently holds just over half of the territory.