WASHINGTON—Ukraine’s leadership warned Wednesday that the likelihood of prolonged conflict against Russian-backed separatists and deadlocked creditor negotiations threaten to derail the West’s $40 billion bailout program.

Ukraine Prime Minister Arseniy Yatsenyuk and Finance Minister Natalie Jaresko, in Washington to win approval for the next payout of International Monetary Fund loans and to seek stronger support from the U.S., said Kiev will likely secure a key tranche of emergency financing from the IMF in early July to help keep the beleaguered economy afloat this year.

Ms. Jaresko said Ukraine’s parliament would move next week to approve three final preconditions for the $1.7 billion IMF payout, including legislation strengthening the independence of the central bank, paving the way for the fund’s board to greenlight the cash next month.

But unless creditors agree to take a loss on their bondholdings, Ukraine’s economy will struggle to right itself. Stalled creditor talks have forced the government to ramp up threats to halt payments.

“If there is no acceptable solution on a consensus basis, we are ready to impose a moratorium,” the prime minister said.