A GFG statement said it would launch legal action against private equity firm AIP, which said it took control of the smelter in Dunkirk, Europe's largest primary aluminium producer, after a default on debt by a unit of GFG.

GFG has been scrambling to refinance its cash-starved web of businesses in steel, aluminium and energy after supply chain finance firm Greensill filed for insolvency in March.

In July GFG said it had agreed a deal with commodities group Glencore to refinance the debt on its aluminium unit after GFG's main lender collapsed.

"Given GFG's efforts to repay, repurchase or refinance the debt, AIP's stated position that GFG is in default is incorrect. GFG will take all necessary legal measures to unwind AIP's actions," GFG's statement said.

GFG did not give details of any specific legal action.

AIP said the transfer of ownership had been approved by French authorities and France's economy and industry ministers last week said they welcomed the prospect of stable ownership.

The operation in Dunkirk produced 284,000 tonnes of aluminium and employed 550 people in 2018. More recent data was not available.

(Reporting by Eric OnstadEditing by David Goodman)