United States Steel Thursday forecast a surprise loss for the fourth quarter, sending its shares down nearly 5% in aftermarket trading. The company expects an adjusted loss of between 29 cents and 25 cents for the quarter, compared with analysts' average estimate of a profit of 16 cents, according to data compiled by LSEG.

U.S. Steel projected its fourth-quarter adjusted core profit to be about $150 million, which is below its prior forecast of $225 million to $275 million.

Steel prices remained depressed and costs related to the ramp up of its Big River 2 (BR2) facility exert pressure on the quarter, while the team works towards increasing prime ton production in its new mill, said CEO David Burritt.

The company added that demand and pricing environment in Europe has been weak.

To meet production volume requirements after an unplanned downtime from a fire, the company is temporality operating three blast furnaces beginning Dec. 7 but expects to return to two blast furnaces by January, U.S. Steel added.

The fourth-quarter core profit for the flat-rolled segment is expected to be lower than the previous quarter due to lower selling prices and volumes, along with increased outage and maintenance activities.

Core profit at its mini mill segment is also expected to be lower than the third quarter due to lower volumes.

The company sees about $30 million in related start-up and one-time construction costs and $20 million in ramp-related impact from BR2.

U.S. Steel looks to steadily ramp to full capacity in 2025.

The company's forecast comes at a time when its $14.9 billion buyout offer by Japanese steelmaker Nippon Steel faces opposition from U.S. government officials over national security concern.