The company, led by Russian tycoon Oleg Deripaska, blamed falling prices and lower output for the sharp downward swing from a year ago that pushed Q2 losses well beyond forecasts.

"Our industry remains in a crisis of its own making with oversupply leading to excess of stock overhanging the market," Deripaska said in a statement.

RUSAL (RUALR.MM)(RUAL.PA), which competes with U.S. aluminum maker Alcoa Inc (AA.N), reported a recurring net loss for the quarter of $208 million, compared with a revised profit of $125 million for the same period a year earlier.

The company had been expected to post a loss of about $142 million, according to seven banks and brokerages polled by Reuters.

RUSAL said on Monday it would cut aluminum output by 357,000 tons, or around 8.5 percent of production, more than previously planned cuts of 7 percent, as it seeks to support prices in the face of a global supply glut. It produced 4.2 million tons of aluminum in 2012.

Top aluminum makers are taking broader action in the face of record global inventories and stubbornly low prices. Alcoa last week suspended production at smelters in Brazil as part of a review of 460,000 tons of capacity.

The price of aluminum, mainly used in transport and packaging, hit four-year lows below $1,800 a ton in late June. Prices have since recovered to $1,945 but are still down more than 6 percent for the year.

Proposed rule changes for industrial metals warehouses and increased scrutiny by regulators could also unleash stored aluminum, adding to the global surplus and putting further downward pressure on prices.

Recurring net profit is defined as adjusted net profit plus the company's net effective share in Russian miner Norilsk Nickel (GMKN.MM).

RUSAL's total net loss in the first half of the year was $439 million, the company said, including a one-off $234 million loss related to a Norilsk Nickel share sale. Shares in Hong Kong-listed Rusal were trading down 4.5 percent at about 0240 GMT on Monday.