President Volodymyr Zelensky has announced the dismissal of Ukraine’s top commander, General Valerii Zaluzhnyi, in the biggest military shakeup since the start of Russia’s full-scale war almost two years ago.

Zelensky’s move follows tensions between Zelensky and his hugely popular military chief after the failure of Ukraine’s much-anticipated counteroffensive.

The move also comes as Ukraine faces a renewed Russian offensive, manpower and ammunition shortages, and much needed US military aid stalled in Congress.

In a Telegram post sent shortly before the announcement, Zelensky said he held a meeting with Zaluzhnyi, and “discussed what kind of renewal the Armed Forces of Ukraine need.”

“The time for such a renewal is now,” Zelensky wrote.

Zaluzhnyi’s replacement will be Oleksandr Syrskyi, who since 2019 has served as the Commander of Ukrainian Land Forces.

Zaluzhnyi wrote on his Telegram channel on Thursday that “the tasks of 2022 are different from those of 2024.

“Therefore, everyone must change and adapt to the new realities as well. [We] have just met with the Supreme Commander-in-Chief. It was an important and serious conversation. It was decided that we need to change our approaches and strategy.”

Rumors of Zaluzhnyi’s dismissal began growing around Kyiv last week after he was called to a meeting at the president’s office and told he was being fired. Zelensky’s office initially denied the rumors, but the move was confirmed on Thursday.

Zaluzhnyi – who had been appointed army chief by Zelensky in July 2021 – was offered a new position by the president, which he turned down. As at press time, it remains unclear whether Zaluzhnyi has decided to remain involved with the military in some capacity.

Differences between the two men has existed for a while as polls say the army chief is the second most popular man in Ukraine after Zelensky and could contest the presidential elections against Zelensky soon.

The tensions appeared to grow wider towards the end of last year, after Zaluzhnyi said the war had reached a stalemate in a long essay and interview in The Economist magazine in November.

He warned that without a great technological leap forward “there will most likely be no deep and beautiful breakthrough,” but instead an equilibrium of devastating losses and destruction.

His remarks drew immediate criticism from Zelensky’s office, which said such commentary about the war only benefitted Russia.

Also recently, the two leaders clashed over whether Ukraine needed a mass mobilization effort. The army chief had suggested up to half a million draftees were required, which Zelensky resisted.

The president told a press conference in December that mobilization was a ‘highly sensitive’ issue and that he wanted to hear more arguments in favor before he felt fully ready to back the move.

“This is a very serious number,” Zelensky said. “It is a question about people, about justice, about defense capabilities. It is also a financial question.”

When Russia launched its invasion in February 2022, many of Ukraine’s allies feared Kyiv would fall in just a few days and the rest of the country within weeks. But Ukraine’s troops, under Zaluzhnyi’s direction, were able to drive Moscow’s forces from the capital and later in the year managed to reclaim large parts of the southern and eastern territories occupied by Russia in the early weeks of the war.

Ukraine had hoped to drive Moscow’s forces back further in 2023 but battlefield success proved elusive.

The counteroffensive launched last June, aimed to push south towards the Sea of Azov, splitting Russia’s forces in two and cutting its land bridge to Crimea.

But Ukraine’s forces attempted to advance from Orikhiv towards Tokmak, but only made it as far as Robotyne, a little over 20 kilometers (12.4 miles) south. Russia still occupies around a fifth of Ukraine’s territory.

Zaluzhnyi will now be replaced by the 59-year-old Syrskyi, who began his soldiering career during the last years of the Soviet Union, training in Moscow.