Ukraine's president Volodymyr Zelenskyy has defended his decision to dismiss popular defence minister Mykhailo Fedorov and confirmed reports of a breakdown in relations between the ministry and the country's top army leadership. This was reported by Qazaqyia.kz citing The Guardian.

Speaking at a press conference in Kyiv with the British prime minister, Keir Starmer, Zelenskyy said there had been a "challenging dialogue" between Fedorov – widely seen as a reformist and moderniser – and the military's commander in chief, Col Gen Oleksandr Syrskyi.

"I would very much like to see unity. The sides have not found it. And the problem lies not only with the sides, but with me as well," Zelenskyy said. "But things are as they are. And in such a situation, you have a choice: either one side or the other."

He has appointed the acting head of Ukraine's security service, Yevhenii Khmara, as acting defence minister and asked parliament to approve him in the position.

Zelenskyy's decision to back Syrskyi has outraged civil society and dismayed Ukraine's foreign partners. More than 1,000 protesters gathered outside the presidential office in Kyiv on Thursday, carrying placards in support of Fedorov. One read: "For what?". Another said: "Is your head screwed on?" There were loud chants of "Syrskyi out".

It was only the second time since Vladimir Putin's 2022 invasion that large numbers of people have taken to the streets in anti-government protests. A year ago, Zelenskyy's decision – later reversed – to close two anti-corruption agencies provoked a similar backlash.

The growing domestic political crisis overshadowed Starmer's farewell visit to Kyiv, ahead of his departure on Monday from Downing Street. The two leaders laid wreaths at the Wall of Remembrance before holding one-on-one talks in the garden of the presidential palace.

At a joint press conference, Zelenskyy awarded Starmer the Order of Freedom, Ukraine's highest foreign honour. Starmer, who appeared to be close to tears, gave Zelenskyy a framed Ukrainian flag that had hung above Downing Street in February 2022 as Russian tanks rolled towards Kyiv.

Starmer said he would soon depart the political stage but "the support of the United Kingdom for this course will never change". He added: "It is in our bones. The flags are flying in churches and town halls across the country, as they have throughout the duration of this conflict. Your fight is our fight."

The UK prime minister said Ukrainian drone strikes on long-range targets inside Russia had shifted the war's momentum. Putin was "losing", he said. He described the more optimistic mood in Ukraine over the last six or seven months as significant. "It's down to hard work, guts, resolve and courage," he said.

Zelenskyy praised Starmer for leading the coalition of the willing, alongside France, and thanked ordinary Britons for their backing. Asked if the frequent turnover of British prime ministers was a problem for Ukraine, Zelenskyy said "strong relations" with the UK would continue.

Without mentioning Andy Burnham by name, he said he hoped to meet Starmer's successor "as soon as possible". Starmer and Zelenskyy then embraced warmly, patting each other on the arm, and walked back into the neoclassical, turquoise-painted palace for an official lunch.

Meanwhile, Fedorov addressed his own press conference, accusing Ukraine's top brass of obstructing reforms and using Soviet-style methods. He said decisions on which military brigades to support – including with drones – were made on the basis of "loyalty" rather than data. "It's impossible to develop the system on this basis," he said.

He said Ukraine's general staff had opposed his plans to create centres of excellence and change the army's organisational structure. Instead, it had blocked initiatives and engaged in "bureaucratic wrangling". Fedorov said he had proposed replacing Syrskyi – a suggestion that appears to have led to his own dismissal on Wednesday.

"This sort of culture needs to be eradicated, because otherwise we won't be able to defeat an enemy whose system is plagued by the very same issues," he said. "We have no other choice if we want to defeat Russia asymmetrically, with minimal losses."

Fedorov said he had turned down an offer from Zelenskyy to stay on as a government adviser. On Wednesday, Ukraine's parliament accepted the resignation of the prime minister, Yulia Svyrydenko, after Zelenskyy said his government needed a reboot. Her replacement is likely to be Serhiy Koretskyi, the head of the energy company Naftogaz.

Fedorov's scathing comments suggest the political crisis in Ukraine is deepening.