A framework agreement outlining U.S. access to revenues from Ukraine's natural resources in exchange for security guarantees has legal gaps that must be filled in future negotiations, four experts told Reuters a day before the countries' leaders meet in Washington.

A draft of the deal seen by Reuters outlines the creation of a joint U.S.-Ukraine-managed "Reconstruction Investment Fund." It contains reassuring language, but the United States does not offer Kyiv the security guarantees it craves.

It is expected to be signed on Friday when U.S. President Donald Trump meets Ukraine's Volodymyr Zelenskiy.

The deal envisages the Ukrainian government contributing 50% of future monetisation of any state-owned natural resource assets to the fund. But it provides no amounts, timeline or details about the fund's management.

That is not surprising and is what would be expected from a framework agreement, said Brian McGarry, assistant professor of international law at Leiden University, who has advised developing states on treaty negotiations.

"It creates obligations to cooperate, but it does not have any binding specific commitments of a defence nature. That is exactly what we see in this agreement. The U.S. has not given concrete assurances," McGarry said.

One diplomatic source, who requested anonymity to discuss sensitive matters, said the document "appears to be a pretty good deal for both sides."

Despite the absence of security guarantees, terms outlined in the framework may come as a relief to Ukraine, with Trump dropping his initial demand for $500 billion in compensation for military support already provided.Zelenskiy said on Wednesday the success of the minerals deal will hinge on talks with Trump, citing its lack of firm U.S. security guarantees.

The document does say that funds will be reinvested "to promote the safety, security and prosperity of Ukraine" to be worked out in a fund agreement that will address future financial distributions.

The U.S. government "will maintain a long-term financial commitment to the development of a stable and economically prosperous Ukraine," the document states, but it does not specify what that means.

McGarry added that details will have to be worked out in future negotiations that could result in a binding treaty.

UNPRECEDENTED APPROACH

One element that stood out to McGarry is that the draft explicitly states that in future negotiations about the fund, Ukraine and the U.S. "will strive to avoid conflicts with Ukraine's obligations" on its path to join the European Union.

"There is at least in principle interesting political support for that process," he said, amid Washington's increasingly antagonistic stance towards the EU.

Ukraine has deposits of 22 of the 34 minerals identified by the EU as critical, including industrial and construction materials, ferroalloy, precious and non-ferrous metals, and some rare earth elements.

Trump's aims appear to be twofold. Recoup Washington's financial and military support for Ukraine since Russia's full-scale invasion three years ago and limit U.S. reliance on Chinese resources.

China, with whom Trump has threatened a trade war, is the world's largest producer of rare earths, which are used to make magnets found in electric vehicles, weaponry and electronics.

The framework agreement makes no reference to a dispute mechanism and Washington's share of a future fund is also left open for discussion, said Duke University international law professor Tim Meyer.

"The agreement demonstrates some uncertainty on the U.S. side about whether the government has the authority to take the kind of interest in the fund that the agreement contemplates," he said, adding that a negotiated fund agreement would likely require congressional approval.

Guillermo Christensen, a national security and international trade expert at U.S. law firm K&L Gates, said the framework offered "a unique and unprecedented approach" not seen in other national agreements.