State-run Saudi Arabian Mining Co. (Maaden) said in a statement that Alcoa's stake was reduced to 25.1 percent from 40 percent and called the move "a rejig in (Maaden's) capital stake in the joint-venture project with Alcoa" without giving more details.

The stake cut corresponds to a reduction of Alcoa's investment to $2.71 billion from $4.32 billion.

Maaden - whose stake in the joint-venture rose to 74.9 percent from 60 percent previously - said the project's size and start date would not be altered because of this change.

Alcoa agreed in December to take the 40 percent stake in the Ras Azzour plant with Maaden after Rio Tinto Alcan abandoned its 49 percent stake about a year earlier in a similar plan with Maaden because Rio Tinto was unable to obtain financing due to the global financial crisis.

The project was then budgeted at $8 billion.

Since its agreement with Alcoa, Maaden has not made any announcements about progress in raising financing for the project which aims to start production from 2013.

The Ras Azzour plan is the biggest of investments Maaden pledged to deliver in 2008 when it raised SR9.25 billion ($2.47 billion) in an IPO that was open only to Saudi investors.

Maaden's deal with Alcoa provided for the setting up of a 1.8 million ton-per-year refinery, a 740,000 ton-per-year smelter, a bauxite mine with an annual capacity of 4 million tons and a rolling mill with a capacity of up to 460,000 tons.

The smelter and mill are slated to start production in 2013 while the refinery and mine would come online in 2014.

Alcoa's Chief Executive Klaus Kleinfeld said in December the $10.8 billion cost of the project would be split, with the US firm and its partners paying 40 percent while Maaden is to handle 60 percent.

Maaden is investing about 60 billion riyals to develop the Kingdom's phosphate, bauxite, gold and industrial minerals and help reduce reliance on oil.