Yemen's former Vice-President and Prime Minister, Khaled Bahah, has denounced his surprise dismissal as a "coup against legitimacy".
President Abdrabbuh Mansour Hadi sacked Mr Bahah on Sunday, citing "failures" in the government's performance.
But on Tuesday, Mr Bahah said the move undermined the cabinet and its work to end the war between pro-government forces and the Houthi rebel movement.
A new round of UN-sponsored peace talks is due to start later this month.
Some 6,300 people, half of them civilians, have been killed since the conflict escalated in March 2015, when Mr Hadi was forced to flee the country and a Saudi-led coalition intervened militarily.
Pro-government and coalition forces have retaken parts of southern Yemen but the rebels and allied army units loyal to long-time former President Ali Abdullah Saleh still control the capital Sanaa.
'Victory for hardliners'
On Sunday, the president announced he had decided to dismiss Mr Bahah because his government had "failed to ease the suffering of our people, resolve their problems and provide their needs", particularly in the "fields of economy, services and security".
He appointed Ahmed Obeid bin Daghr, who was an official in Mr Saleh's former ruling General People's Congress party, as prime minister and Maj Gen Ali Mohsen al-Ahmar, a politically powerful military commander and staunch opponent of the Houthis, as vice-president.
Mr Bahah did not initially criticise the reshuffle, writing on social media on Sunday that he was "opening a new page" in his services to the country as a presidential adviser.
But on Tuesday, he released a lengthy statement explaining that his dismissal would "provide a justification for the coup" by the Houthis and "undermine the legitimacy of the government".
One unnamed Yemeni government official said the shake-up might undermine the peace talks scheduled to start in Kuwait on 18 April.
"Bahah was in favour of a political settlement and the appointment of Ali Mohsen is a victory for the hardline wing," the source told Reuters news agency.