Protesters gathered in downtown Kyiv on Thursday after Ukrainian President Volodymyr Zelensky moved to dismiss his defense minister, as parliament convened to appoint a new prime minister as part of a major government reshuffle.

The shake-up could become a test of Zelensky’s political authority as Ukraine’s fight against Russia’s full-scale invasion approaches four and a half years.

Defense Minister Mykhailo Fedorov, 35, is considered to be a modernizer whose technological expertise is credited in part with a significant improvement in Ukraine’s military performance in recent months against Russia’s bigger army. He was expected to leave the government after just six months in the post.

Zelensky didn’t publicly give a reason for Fedorov’s anticipated exit. Unconfirmed Ukrainian media reports said that Fedorov had a strained relationship with General Oleksandr Syrskyi, the commander of Ukraine’s armed forces.

Syrskyi, 60, is credited with initially organizing the defense of Kyiv in February 2022, and seven months later masterminded a successful counteroffensive in the Kharkiv region. He was born in 1965 in the Soviet Union and attended Moscow Higher Military Command School before serving in the Soviet Artillery Corps.

The mostly young protesters shouted Fedorov’s name and made crude remarks about Skryskyi. They chanted, “Syrskyy go away!” and “A European army for a European country!”

Bohdan Huryak, a Kyiv resident at the protest, said that he was “deeply outraged” by Fedorov’s exit.

“I’m not deeply invested in the internal political debates, but this is a person who shows results on the battlefield, we see results, we feel the fighting spirit and confidence in victory rising,” Huryak said. “And then, six months later, he is removed from office? Come on.”

Demonstrations were also held in other cities across Ukraine, including Dnipro in the center of the country and the southern port city of Odesa.

Zelensky swiftly reversed course in July last year when large street protests broke out over a new law that would have curbed the independence of the country’s anti-corruption watchdogs. The outcry threatened the stability of his leadership for the first time since Russia’s all-out invasion, which began on February 24, 2022.

Before he became defense minister last January, Fedorov was the head of Ukraine’s digital transformation policies and seen as a modernizer. He won public popularity by spearheading Ukraine’s speedy development and deployment of drone technology and introducing several successful e-government platforms.

He also promised sweeping military reforms, saying after he took over that the military had faced about 200,000 troop desertions and draft-dodging by around 2 million people.

Fedorov highlighted in his social media posts what he said were major achievements during his brief tenure. He said that he took the risk of redirecting funds originally earmarked for salary payments into midrange strike capabilities, fiber-optic drones, reconnaissance systems and other technologies.

He also pointed to expanded drone procurement, Patriot missile defense contracts, successful ballistic missile tests and sweeping changes to military procurement.

At the same time, he acknowledged that he was unable to complete the Defense Ministry’s organizational transformation “according to Nato standards and common sense,” move all procurement to competitive tenders, and build a culture of accountability.

He said that while many officials had been dismissed under his authority, “it was necessary to dismiss even more people who were hindering the changes.”

Zelensky didn’t formally announce Fedorov’s departure. However, Fedorov confirmed his dismissal and listed his achievements in office in social media posts late Wednesday, after days of unconfirmed Ukrainian media reports that he was on his way out.

Zelensky also nominated Naftogaz CEO Serhii Koretskyi to take over as prime minister, parliamentary Speaker Ruslan Stefanchuk said in a social media post late Wednesday.

Zelensky said Wednesday that Koretskyi was the most appropriate candidate for the government’s priority of preparing Ukraine for another difficult winter. He cited the Naftogaz chief’s experience in the energy sector.

Lawmakers in Ukraine’s parliament, the Verkhovna Rada, were debating the Cabinet changes before the summer recess begins on Saturday.