Ukraine’s parliament is to try to vote in a replacement for Prime Minister Arseniy Yatsenyuk amid a growing sense of political crisis.
Mr Yatsenyuk announced on Sunday he would resign. His government has been accused of inaction and corruption.
Parliamentary Speaker Volodymyr Groysman has been nominated by President Petro Poroshenko’s party to replace Mr Yatsenyuk.
However, reports late on Monday suggested he may not take the post.
The BBC’s Tom Burridge in Ukraine says that if there is no progress on Tuesday towards the creation of a stable reform-minded government there will be frustration in Berlin and Washington, and satisfaction in Moscow.
The Western-backed reform programme of the government has stalled in recent weeks and several high-profile reformists have left the government.
Economy Minister Aivaras Abromavicius resigned more than two months ago after accusing the government of not being committed enough to end corruption.
Mr Yatsenyuk has been in office since former pro-Russian President Viktor Yanukovych was ousted during huge demonstrations in February 2014.
Announcing his resignation on Sunday, Mr Yatsenyuk accused Ukraine’s politicians of failing to enact “real changes”.
His loss of parliamentary support led to him being asked by President Poroshenko to resign in February amid complaints of government inaction and corruption. Although he survived a vote of confidence he has remained unpopular in the polls.
The initial plan was that Mr Yatsenyuk would be succeeded by Mr Groysman, an ally of the president.
But disagreements over key posts in the new cabinet have led Mr Groysman to turn down the job, two prominent MPs said on Monday evening.
That means it is not clear who will succeed Mr Yatsenyuk when he officially tenders his resignation.
The latest crisis comes as the International Monetary Fund (IMF) has threatened to withhold aid money if Ukraine does not carry out reforms.
The government in Kiev is signed up to an uneasy truce with pro-Russian rebels in two of Ukraine’s eastern regions, with frequent ceasefire violations reported.
Russia annexed the southern region of Crimea two years ago after a controversial referendum on self-determination.
Ukraine’s ambitions to join the EU also suffered a setback on 6 April when voters in the Netherlands roundly rejected a landmark EU trade deal with the former Soviet state in a referendum.