In the letters, seen by Reuters, Alcoa expressed concerns that large amounts of Russian aluminium flowing into the LME's warehouses could distort the exchange's aluminium contract by making it reflect the price of unwanted material.

While Russia has escaped official sanctions on its aluminium, copper, and nickel of the kind imposed on some sectors following its invasion of Ukraine, some Western companies have stopped accepting Russian metal.

Alcoa is one of several U.S. and European metals producers that have lobbied for the LME and Western governments to restrict trade in it.

In a letter to the LME dated Sept. 29 and signed by chief commercial officer Kelly Thomas, Alcoa said it and most of its customers had stopped accepting Russian material.

It said that without buyers, more metal made by Russian aluminium producer Rusal could be deposited on the exchange, which functions as a market of last resort, leaving the LME with stocks that Alcoa said many companies and banks may not want to deal with.

"As we move into 2023 ... it is easy to see a scenario where well over one million metric tons per year of Rusal metal could be put on warrant," it said.

"The LME aluminium contract will be distorted because it will disproportionately reflect the discounted value of the Rusal brand."

The LME declined to comment on the letters. Rusal said last week its aluminium remains in demand.

Letters sent by Alcoa to the LME dated Oct. 18 and Oct. 27 said around 250,000 tonnes of aluminium that entered LME-registered warehouses in October could be Russian, and asked the LME to publish daily disclosures showing how much Russian metal was in its system.

Alcoa said it had not received a response to its request.

"Alcoa urges the LME to immediately delist all Russian brands, regardless of the production date," the company said in its Oct. 27 letter.

(Reporting by Peter Hobson; Editing by Jan Harvey)

By Peter Hobson