At least four Ukrainian officials submitted their resignations on Tuesday ahead of an anticipated government reshuffle, according to the speaker's office.
Their requests will be considered in the next parliamentary session, parliamentary speaker Ruslan Stefanchuk wrote on Facebook.
The ministers who tendered their resignations were: Minister of Strategic Industries Oleksandr Kamyshin, Deputy Prime Minister for European Affairs Olga Stefanishyna, Minister of Justice Denys Maliuska, and Minister of the Environment Ruslan Strilets.
Zelenskyy also dismissed Rostyslav Shurma, one of his deputy chiefs of staff whose portfolio is the economy, according to a decree published on the presidential website.
David Arakhamia, a senior lawmaker for Zelenskyy's party, said there would be a "major government reset" that would see more than half of the ministers change.
"As promised, a major government reset can be expected this week. More than 50 percent of the Cabinet of Ministers' staff will be changed," he wrote on Telegram.
"Tomorrow we will have a day of dismissals, and the day after that a day of appointments," he said.
Lawmakers and political analysts have expected major changes in the government since the summer began.
Prime Minister Denys Shmyhal has suggested the possibility of streamlining the government and folding several portfolios into one ministry.
Death toll in Russian missile attack rises to more than 50
Ukrainian President Volodymyr Zelenskyy said in his nightly address that the Russian strike on the city of Poltava Tuesday killed at least 51 people, with more than 270 injured.
Earlier, Poltava Governor Philip Pronin said on messaging platform Telegram that 49 had been killed, with 219 injured.
"Search teams continue to dismantle the rubble at the site," Pronin said.
Germany condemns Poltava attack, says 'Putin knows no limits to brutality'
German Foreign Minister Annalena Baerbock strongly condemned Russia's attack on the Ukrainian city of Poltava. Officials have called it the single deadliest Russian strike this year.
"[Russian President Vladimir] Putin knows no limits to brutality," Baerbock said of the attack, which has killed more than 45 and injured over 200. "He should be held accountable."
Ukrenergo board members resign, protesting 'politically motivated' dismissal of boss
Two members of the supervisory board of Ukraine's electricity grid operator, announced their resignation on Tuesday.
Chairman of the board Daniel Dobbeni and board member Peder Andreasen said in a statement published on Telegram that they believed the decision to dismiss the head of Ukrenergo, Vadym Kudrytskyi, was "politically motivated" and "unacceptable."
A move to dismiss Kudrytskyi was first reported by Forbes Ukraine and other outlets in Ukraine late last week; the Ukrenergo board voted by majority in favor of the move on Tuesday.
Dobbeni and Andreasen said they had submitted their resignation earlier on Wednesday.
"We strongly believe that the decision on the early dismissal of the CEO of Ukrenergo is politically motivated and, based on the results of the presented report, there are no valid grounds for it," they said.
They argued it could also imperil support and cooperation with other European companies for Ukrenergo.
Russian attacks on Ukraine have often targeted its energy infrastructure and substations, with the government calling on the operator to improve security at such sites.
Kudrytskyi also commented on the matter on Wednesday.
"The decision of the Supervisory Board to dismiss me has nothing to do with the security of Ukrenergo's substations," Kudrytskyi said, adding that while he couldn't go into details, aerial defense gear had been installed "almost at every substation."
He said Ukrenergo had fallen victim of anonymous Telegram channels and some media outlets looking to discredit it.