On Thursday, the Kryvyi Rih mill in central Ukraine said the protest linked in part to salary demands had disrupted steelmaking and rolling and paralysed the plant's operations.

After a four-day strike, railway workers have resumed their shifts, ArcelorMittal Kryvyi Rih said in a statement.

"The business is preparing for a gradual restoration of the full metallurgical cycle," it said.

It did not say what overall impact the strike would have on its financial performance or output, which amounted to 6.1 million tonnes of pig iron, 7 million tonnes of steel and 5.5 million tonnes of rolled products in 2016.

ArcelorMittal, the world's largest steelmaker, has invested around $9 billion in Kryvyi Rih since its acquisition in 2005, making it the biggest foreign investor in Ukraine.

Last Thursday it warned that plans to invest another $1.5 billion until 2022 could be at risk due to the strike.

(Reporting by Alessandra Prentice; Editing by Dale Hudson)