Supporters say that concentrating political power is necessary during war.

In the opening months of the war, Mr Zelensky largely kept senior political and military figures in place.

But in May last year, he fired defence minister Oleksii Reznikov after a series of corruption scandals, then sacked Kyiv's top military commander Valerii Zaluzhnyi earlier this year.

In his nightly address from Kyiv, President Zelensky justified the changes, telling Ukrainians that he wanted his government to be "more active" in securing aid from the country's Western allies.

Mr Sybiha will replace Dmytro Kuleba at the foreign ministry, but his appointment is not expected to alter policy significantly. President Zelensky and his office have broadly overseen international relations from the presidential palace.

The ex-ambassador is seen by some as being closer to Andriy Yermak, the increasingly powerful presidential chief of staff. Mr Yermak was said to have clashed with Mr Kuleba.

Another key adviser to the president, Oleksiy Kuleba, has been appointed as deputy prime minister in charge of reconstruction, regions and infrastructure. He previously served as deputy head of the presidential office.

Other changes include the promotion of 38-year-old Olha Stefanyshyna. She has been reappointed as deputy prime minister in charge of European integration, while also being handed the justice portfolio.

Analysts say the move represents Ukraine's desire to move forward with its bid for EU membership. She told MPs on Wednesday that "hundreds and thousands" of legal changes are needed before Kyiv can become a member of the bloc.

Meanwhile, Herman Smetanin, 32, has been appointed strategic industries minister in charge of domestic arms production, a key position as Kyiv's forces face intense Russian attacks in the eastern Donetsk region, while continuing their incursion into Russia's Kursk border province.

Speaking to the BBC on Wednesday, MP Inna Sovsun echoed the president in saying the reshuffle was "the best way to bring in new people, new ideas into the government".

But Dmytro Razumkov, a former ally of Mr Zelensky's turned opposition MP, said the new changes would have little impact on decision-making, claiming in a Telegram post on Thursday that the "Cabinet of Ministers has not influenced anything for a long time".

Another opposition MP, Iryna Gerashchenko, accused Mr Zelensky of "breaking parliamentary tradition" by not being present at votes to approve his new ministers.

She said that the nomination of key posts, such as that of foreign minister, were a "presidential prerogative", adding that "always the presidents represented their candidates".

Oleksandr Merezhko, a lawmaker with Mr Zelesnky's Servant of the People Party, rejected the concerns, noting that the president has always been quick to dismiss ministers who were not meeting his expectation, citing the early dismissal of his first Prime Minister Oleksiy Honcharuk after less than a year in office.

"He came from the sphere of business and he is himself a result-orientated person," Mr Merezhko told the BBC.

"When Zelensky sees someone can't deliver, he will make a change," he added, noting some of ministers dismissed this week were "professionally exhausted".

Prime Minister Denys Shmyhal welcomed the new appointments, acknowledging that they faced "difficult tasks," but insisted that "their experience and skills will help in the implementation of our state's strategic goals".

Under martial law, Mr Zelensky boasts considerable executive powers. With elections suspended while the war continues, and the Servant of the People Party maintaining a parliamentary majority, there is a limited check on his government, some experts say.

But Mr Merezhko dismissed concerns of an over-centralisation of power around Mr Zeleasnky's office.

"In a state of war, some kind of concentration of power is a necessity," he told the BBC. "After all he is the commander-in-chief and we are waging a war, the whole state is like an army right now."

"The challenge for us, and we are coping with this challenge so far, is to preserve democracy and pluralism."