A leading US bank has frozen $22 billion worth of assets belonging to Kazakhstan’s sovereign fund amid a long-running legal dispute between Astana and a pair of Moldovan investors, Reuters news agency reported on December 21.

Reuters cited an unnamed source familiar with the issue as saying that the asset freeze by the Bank of New York Mellon was instigated as a result of a lawsuit filed by Anatolie Stati.

Stati and his son, Gabriel Stati, have been embroiled in a legal campaign for many years to seek compensation for what they claim was Kazakhstan’s efforts to expropriate their investments in two oil and gas fields. The businessmen claim government harassment included groundless tax inspections and arrests of people working for their companies.

It is not yet clear quite why such a large chunk of assets have been sequestered, however.

A tribunal at the Stockholm Chamber of Commerce in December 2013 ruled that Kazakhstan should pay the Statis damages of more than $500 million — that being the claimed value of the investments in question. The businessmen entered Kazakhstan in the late 1990s, when they bought up two companies — Ascom Group SA and Terra Raf Trans — that owned licenses to idle oil and gas fields in the west of the country called Borankol and Tolkyn.

The Statis maintain they invested up to a billion dollars into successfully reviving the fields and that, if anything, the Stockholm arbitration award was nowhere near generous enough.

The entire saga has since dragged on through a variety of other legal fora, now seemingly resulting in this asset freeze, which Reuters estimates represents 40 percent of Kazakhstan’s National Fund.

Reuters also reported that Kazakhstan’s National Bank has responded to the legal onslaught by filing its own lawsuit against BNY Mellon in British courts. The agency’s source said a ruling on that case was being expected on December 21.

Aidan Karibzhanov, a prominent businessman in Kazakhstan, noted that although the $22 billion headline figure might appear alarming, this almost certainly constituted a substantial overreach.

“If fate decrees that the case against [Stati] is to be lost (which is not yet evident), then we are talking about $500 million. The remaining $21.5 billion will be returned nicely nicely,” Karibzhanov wrote on his Facebook account.