Shelling in eastern Ukraine has damaged a key gas pipeline.
The gas transport company Ukrtransgaz said gas supplies would be cut to three towns -- including the port city of Mariupol -- as repair work, expected to take up to two days, is carried out.
The company said in a statement on June 12 that gas supplies to Europe would not be affected.
The Ukrainian Interior Ministry accused pro-Russian rebels of shelling the pipeline.
Prime Minister Arseniy Yatsenyuk accused the separatists of trying to destabilize government-controlled Mariupol.
Rebel officials denied responsibility for the attack on the pipeline around 100 kilometers north of the city on the shore of the Sea of Azoz.
Mariupol is home to two of Ukraine's largest steel plants belonging to steelmaker Metinvest.
Metinvest said in a statement on June 12 that the situation was "critical" and that it was considering whether to temporarily suspend some of its operations.