LONDON (AP) — The death toll from a fire at a coal mine in Kazakhstan rose to 42 on Sunday, with four people still missing, the press service of Kazakhstan’s Ministry of Emergency Situations said.

It added that rescue operations were being “hampered by the presence of destroyed mining equipment, as well as rubble in some places.”

The fire broke out on Saturday at the Kostenko mine, which is owned by Luxembourg-based steel giant ArcelorMittal and located in Kazakhstan’s Karaganda region.

ArcelorMittal said the blaze was believed to have been caused by a blast of methane gas, and that some 252 people were working at the mine at the time of the fire.

It is the latest in a string of workplace deaths at sites operated by ArcelorMittal Temirtau, the local unit of ArcelorMittal that operates the country’s largest steel plants and several coal and ore mines. In August, four miners were killed after a fire erupted at the same mine, while five people died following a methane leak at another site in November 2022.

Following the latest fire, Kazakhstan announced the nationalization of ArcelorMittal Temirtau.

Prime Minister Alikhan Smailov said in a statement on the Kazakh president’s website that the government had reached a preliminary agreement with the company’s shareholders and was now in the process of “formalizing” the nationalization.

Speculation around the company’s future had been growing since September, when Kazakhstan’s first deputy prime minister, Roman Sklyar, told journalists that the government had started talks with potential investors to buy out ArcelorMittal after becoming increasingly unhappy with its failure to meet investment obligations and repeated worker safety violations.

Kazakh President Kassym-Jomart Tokayev declared Sunday a national day of mourning. The office of the country’s prosecutor-general said it was starting an investigation into potential safety violations in the coal mine.

In a statement, ArcelorMittal Temirtau said that work had been halted at all of its coal mining sites in Kazakhstan. It also conveyed “pain” at the lives lost and said its efforts “are now aimed at ensuring that affected employees receive comprehensive care and rehabilitation, as well as close cooperation with government authorities.”