Emboldened by sophisticated weapons and long-range artillery provided by the West, Ukraine went on the offensive against Russian forces in northeast Ukraine on Friday, seeking to drive them back from outside two critical cities.

The stepped-up efforts come as the conflict is increasingly becoming a brutal war of attrition, with a gruelling battle for control over territory in the east.

Neither side has been able to score a major breakthrough, with one taking a few villages one day in one area, only to lose just as many along a different part of the 300-mile-long front.

Ukrainian officials are bracing for what they fear could be even more intense Russian assaults over the weekend, as President Vladimir V. Putin of Russia seeks to claim a victory to showcase on Monday, when Russia celebrates Victory Day, an annual holiday marking the Soviet defeat of Nazi Germany.

Local leaders announced new curfews and issued urgent warnings about the threat of increased Russian missile strikes.

New York Times News Service