President Volodymyr Zelenskiy replaced Ukraine's popular army chief with his ground forces commander on Thursday, a huge gamble at a time when Russian forces are gaining the upper hand nearly two years into their war.

The shakeup ushering in a new military leadership follows months of speculation about a rift between Zelenskiy and army chief General Valeriy Zaluzhnyi, who many Ukrainians see as a national hero.

“As of today, a new management team takes over the leadership of the Armed Forces of Ukraine,” Zelenskiy said in a statement.

He promoted ground forces chief Colonel General Oleksandr Syrskyi, 58, to be the new head of the Armed Forces, citing his role in overseeing the defence of Kyiv in 2022 and the lightning Kharkiv counteroffensive later that year.

Syrskyi, who goes by the call sign “snow leopard”, takes the helm amid deep uncertainty as Kyiv awaits vital military aid from the United States that has been delayed by Republicans in the U.S. Congress for months.

The U.S. State Department said the move to replace Zaluzhnyi was a “sovereign decision”.

The Pentagon said Washington “will work effectively with General Syrskyi, we already have”.

With Ukraine struggling to overhaul how it mobilises civilians into the army, the sacking of Zaluzhnyi could deal a blow to troop morale on a 1,000-kilometre (621-mile) front. It could also backfire politically, hurting Zelenskiy's ratings.

Zelenskiy said he was grateful to Zaluzhnyi for his time as army chief and posted a photograph of the two men shaking hands and smiling, with Zaluzhnyi flashing the peace sign.

Messages of gratitude

Messages of gratitude for Zaluzhnyi, known widely as the “Iron General”, flooded social media following the announcement. Some Ukrainians posted images of the top general alongside images of hearts.

Passers-by in central Kyiv openly questioned the move.

“This is a very odd decision. We know our enemy and it is not Zaluzhnyi,” said Svitlana Kalinina, a consultant.

“I am very upset. I don’t know about others but I am very upset. This is a signal that worries me,” said Olena, a doctor.

Late last year a poll put the public’s trust in Zaluzhnyi at over 90%, significantly higher than Zelenskiy’s 77%.

Under Zaluzhnyi’s command, Ukrainian forces rebuffed Russia’s initial assault on Kyiv and reclaimed swathes of territory in 2022. But the battlefield momentum turned against Ukraine last year as a much-vaunted counteroffensive proved unable to break through heavily defended Russian lines.

Russia has since ramped up offensive pressure on the eastern front, trying to cut off and encircle the town of Avdiivka.

Zelenskiy indicated it was last year’s setback that underpinned his decision to replace Zaluzhnyi.

“In the second year of this war, we won the Black Sea. We won the winter. We proved that we can regain control over the Ukrainian sky. But, unfortunately, we could not achieve the goals of our state on the ground.”

The military shakeup unfolded over a series of statements in which Zelenskiy said he had met Zaluzhnyi to discuss changes to the military leadership, adding that he had asked the general to remain “on his team.”

In a separate statement, Zaluzhnyi said he had met Zelenskyi for an “important and serious conversation” and that a decision had been made to change battlefield tactics and strategy.

“The tasks of 2022 are different from the tasks of 2024. Therefore, everyone must change and adapt to new realities as well. To win together too,” his statement said.

The two statements were published within moments of one another, suggesting that the two most prominent wartime figures in Ukraine had coordinated closely to put on a display of unity.

As ground commander, the new army chief Syrskyi is also closely associated both with Ukraine’s initial successes and its more recent setbacks. In an interview with Reuters last month, he signalled the importance of rotating out exhausted troops who have been under near-constant artillery fire.

“Our task and...one of the reasons for the attention on mobilisation is the timely replenishment of those units that are head for replacement.”