International Monetary Fund chief Christine Lagarde suggested Wednesday that the fund's programme in Ukraine might not continue unless that country ramps up measures to fight corruption.
Ukraine's economy minister stepped down last week, saying his work was being blocked by corrupt senior officials.
"Without a substantial new effort to invigorate governance reforms and fight corruption, it is hard to see how the IMF-supported programme can continue and be successful," Lagarde said in a statement.
She said Ukraine has made slow progress in "fighting corruption and reducing the influence of vested interests in policymaking."
Last week, Lagarde praised the departing economy minister, Aivaras Abromavicius, saying he "conducted some really good and solid reforms," including measures to encourage direct investment in the country.
Lithuanian-born Abromavicius was appointed in December 2014, after Ukraine ousted its former pro-Russian president amid mass protests calling for closer ties with the West. Ukraine also appointed a US-born finance minister, Natalie Jaresko, on the same day.
Upon announcing his resignation, Abromavicius singled out a close ally of current President Petro Poroshenko - federal lawmaker Igor Kononenko - as one of the officials working "behind my back."
Poroshenko has become significantly unpopular as Ukrainians increasingly believe he has failed to improve the country, according to US-based pollster Gallup.
His approval rating among the Ukrainian people dropped to a meagre 17 per cent, well below the 28 per cent that his pro-Russian predecessor Viktor Yanukovych had before being ousted, the pollster said in December.
International funding is crucial for cash-strapped Ukraine to stave off bankruptcy as it struggles to bring its economy out of Russia's direct influence and quell a pro-Russian separatist rebellion in its east.
Jaresko said last month that the country expected up to 10 billion dollars in foreign funding this year. The IMF planned to soon extend at least 1.7 billion dollars in credit to Ukraine for the country to replenish its gold reserves, state news agency Ukrinform reported at the time.