(Bloomberg) -- The overseas arm of Russian coal company UK Kuzbassrazrezugol AO has asked clients to defer deliveries as Covid-19 causes staff shortages on the country’s railways.

In a letter to clients seen by Bloomberg News, the company asked for deliveries planned for the first two quarters of this year to be delayed by one quarter respectively. The company cited widespread illness due to the spread of the omicron variant among staff of the railway used to transport the coal.

“Without prejudice to our rights and obligations we kindly ask you to consider postponing the deliveries previously planned,” Roman Ershov, director of Cyprus-based KRU Overseas Ltd., said in the letter dated Feb. 18.

Coal prices have soared across the world after a temporary export ban from Indonesia earlier this year upended markets. Miners from Australia to Colombia are also facing pandemic-related disruptions, while Russia, which accounts for almost 20% of the global trade, is facing logistical constraints.

Tensions between the West and Russia over Ukraine are also boosting prices, as European electricity producers are increasingly turning to coal for power generation on concerns about disruptions to natural gas supplies. Coal futures in Europe have risen over 14% since Friday’s market close, with the continent’s stockpiles falling to their lowest ever recorded.

The volume of cargo dispatched from Russian railway stations and transported to ports has fallen by 60% compared to the same period in previous years, due to “critical staff shortages” at Russian Railways JSC, KRU said in the letter. The “situation is the same for all coal producers in Russia,” it added.

KRU didn’t respond to a request for comment on the letter during a public holiday in Russia. The Cyprus unit also didn’t return a request for comment.

Russia is the world’s third largest exporter of thermal coal, behind Indonesia and Australia. The country accounted for 18% of global coal trade in 2020, according to the International Energy Agency. 

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