Russian aluminum giant Rusal is concerned about an impending catastrophe if U.S. sanctions are not lifted, with some of its production halted as early as September, two sources close to the company said.

Under the terms of the sanctions, imposed in April in response to Moscow's alleged meddling in the 2016 U.S. election, U.S. customers must wind down business with Rusal by Oct. 23.

"If sanctions are not lifted in the near future, then contracts will expire and from Oct. 1, all of the company's production, intended for the external market, will once again go into the warehouses," a source close to Rusal said.