The amount represents one-fifth of the foreign reserves held by Africa's largest economy.

The Process and Industrial Developments Limited (P&ID;) company -- widely reported to be registered in the British Virgin Islands -- was founded by two Irish business partners for the purpose of executing the 2010 deal with the Lagos government.

The 20-year agreement would see P&ID; "build a state-of-the-art gas processing plant to refine natural gas... (which) Nigeria would receive free of charge to power its national electric grid," according to the P&ID; website.

The company intended to sell the byproducts from the process on the global market for "profits in the billions of dollars," P&ID; said.

London court documents released on Friday showed that the arrangement fell through in 2012.

An arbitration tribunal in England awarded the firm $6.6 billion (5.9 billion euros) in damages in January 2017.

P&ID; said accrued interest had pushed that amount to more than $9 billion -- about one-fifth of Nigeria's declared foreign reserves of $45 billion.

The Nigerian government's legal team argued that English courts did not have the jurisdiction to settle the dispute.

It added that the settlement was "manifestly excessive and penal," according to court documents.

But Justice Christopher Butcher of the Commercial Court in London ruled on Friday that he was "prepared to make an order enforcing the final award".

"I will receive submissions from the parties as to the precise form of order appropriate," the justice wrote in his conclusion.

A lawyer representing P&ID; said the firm intended to "begin the process of seizing Nigerian assets in order to satisfy this award as soon as possible," the Bloomberg news agency reported.

The Nigeria government issued no immediate comment.