Ukrainian President Volodymyr Zelenskyy is thought to have taken one of his “biggest gambles” yet by replacing his top commander in a dramatic military shake-up.

Col. Gen. Oleksandr Syrskyi, one of Ukraine’s most experienced commanders who had led the country’s ground forces since 2019, was on Thursday appointed the new head of Ukraine’s armed forces amid broader military leadership changes.

Zelenskyy removed Gen. Valeriy Zaluzhnyi, a widely respected and popular figure in Ukraine, following months of speculation about his future and reported tensions between Zelenskyy and Zaluzhnyi over strategy.

It represents the most significant change to Ukraine’s military leadership since Russia launched its full-scale invasion of the country nearly two years ago.

In a post on social media platform X, Zelenskyy said he had taken the decision “to renew the leadership” of Ukraine’s armed forces and thanked Zaluzhnyi for his two years of service.

“I appreciate every victory we have achieved together, thanks to all the Ukrainian warriors who are heroically carrying this war on their shoulders. We candidly discussed issues in the army that require change. Urgent change,” Zelenskyy said.

“This is not about surnames, and surely not about politics,” Zelenskyy said. “This is about our army system, about the management of the Armed Forces of Ukraine, and about involving the experience of this war’s combat-hardened commanders.”

Zelenskky concluded the announcement by saying “2024 can be successful for Ukraine only if there are effective changes in the basis of our defense, which is the Armed Forces of Ukraine.”

Zaluzhnyi, dubbed the “iron general,” was credited for playing a pivotal role in Ukraine’s surprise defensive stand against Russia during the early months of the war and came to be seen as a symbol of Ukraine’s fighting spirit.

However, a reported rift between Zelenskky and Zaluzhnyi went public late last year when the latter said in an editorial in The Economist that the war had reached a stalemate. Zelenskky later rebuked Zaluzhnyi for that assessment and denied the war was at an impasse.

“While Zelenskyy’s decision to dismiss Zaluzhny comes as no surprise, it is one of the Ukrainian leader’s biggest gambles of the entire war,” Peter Dickinson, editor of the Atlantic Council think tank’s UkraineAlert service, said in a blog post.

Dickinson said there was an obvious need for a change in tactics given that Ukraine’s forces had been unable to achieve major breakthroughs on the battlefield for some time. However, he warned that the timing of Zaluzhny’s removal appeared to be “particularly unfortunate.”

“Ukraine currently faces growing ammunition shortages amid alarming delays in Western military aid. This is already placing severe constraints on any offensive operations and has left Ukrainian commanders with little choice but to switch to active defense,” Dickinson said.

“If the military situation deteriorates further in the coming months, Zelenskyy will now find that he is held personally responsible,” he added.

Syrskyi, the new head of Ukraine’s armed forces, oversaw many of the country’s most notable successes of the past two years. These include the defense of the capital Kyiv in the first month of Russia’s full-scale invasion and the Kharkiv counteroffensive in September 2022.

Syrskyi has, however, also faced criticism for his role in the battle to defend Ukraine’s eastern city of Bakhmut, with both Russia and Ukraine reporting heavy casualties in the fighting.

Andrius Tursa, Central and Eastern Europe Advisor at consultancy firm Teneo, said Zelenskyy’s move to replace his top military commander “will likely turn out to be an unpopular decision.”

“Zaluzhnyi’s dismissal is widely perceived as an attempt by Zelensky to sideline a potential political competitor. This suggests a prioritization of his own political goals over the country’s wider interests at this difficult phase of the war,” Tursa said Friday in a research note.

“From the perspective of Kyiv’s international allies, the questionable replacement of the military leader, along with Zelensky’s hints at a wider political reshuffle, broadcasts a message of divisions and competition at the highest levels.”

Tursa said these optics would not help Ukraine at a time when its allies “are already struggling to find consensus on continued assistance.”

Analysts at the Institute for the Study of War said Thursday that military leadership changes were normal for states locked in a protracted war.

The think tank said Zelenskyy, Zaluzhny and Ukrainian Defense Minister Rustem Umerov had all previously acknowledged that the war had changed dramatically between 2022 and 2024 and that new approaches and strategies were necessary.