Russia unleashed a string of attacks against Ukrainian rail and fuel facilities Monday, striking crucial infrastructure far from the front line of its eastern offensive, which Britain said has yet to achieve a significant breakthrough.

Meanwhile, two fires were reported at oil facilities in western Russia. It was not clear what caused the blazes.

As both sides in the 2-month-old war brace for what could be a grinding battle of attrition in the country’s eastern industrial heartland, top American officials pledged more help to ensure Ukraine prevails.