WASHINGTON—A senior International Monetary Fund official Wednesday said it can't help Europe with fresh emergency financing for Greece because Athens's creditors haven't yet committed to detailed debt relief.

The comments show that the agreement touted by European finance ministers last night to release fresh bailout cash for Greece hasn't nailed down the key elements the IMF says are critical to finally return the debt-laden country to health. Rather, the IMF's reserved support for the deal has paved the way for Germany to approve new funds and sets the stage for more tough negotiations later this year.

"Fundamentally, we need to be assured that the universe of measures that Europe will to commit to…is consistent with what we think is needed to reduce debt," the senior official told reporters on a conference call. "We do not yet have that."

But the official said Europe's acknowledgment that debt relief is needed and would be detailed later this year was enough to win the fund's conditional backing.

"All the stakeholders now recognize that Greek debt is…highly unsustainable," the official said. "They accept that debt relief is needed, they accept the methodology that is needed to calibrate the necessary debt relief. They accept the objectives of gross financing needs in the near term and in the long run. They even accept the time tables."

Many outside economists see the deal as papering over the differences and once again prolonging the crisis.

"Summary of Eurogroup: Germany always wins, IMF caves under pressure from Germany and U.S., no one does what's in Greece's best interests," said Megan Greene, chief economist at Manulife and John Hancock Asset Management, in a tweet.

Marc Chandler, global head of currency strategy at investment bank Brown Brothers Harriman, called the deal a "paper charade" that saves Europe more than it does Greece.

The IMF and its largest shareholders, Europe and the U.S., were concerned that failure to reach a Greek deal could give proponents of a U.K. exit from the European Union leverage ahead of a referendum next week.

"It chose to capitulate now and fight later," Mr. Chandler said. "Its capitulation was to sign off on the agreement even though the debt relief that it had insisted on as a precondition is a little more than vague suggestions until the end of the current program."

Write to Ian Talley at ian.talley@wsj.com

(END) Dow Jones Newswires

May 25, 2016 12:35 ET (16:35 GMT)