Russian forces are attempting another crossing of a river where they suffered a major blow, Ukraine’s military says.

Russia’s military prepared on Saturday to attempt another pontoon crossing of an eastern Ukrainian river that has posed a formidable barrier to its aims in the region, Ukraine’s military said, despite suffering one of its single most lethal engagements of the war in a previous attempt this month.

Russian forces were staging bridging equipment again near the Seversky Donets River, the Ukrainian military said in its regularly published morning assessment of the war. It said the Russian military appeared ready to resume an offensive in the area directed at the town of Yampil.

“The enemy has not ceased offensive actions in the eastern operation zone with the goal of establishing full control over the territory of the Donetsk and Luhansk regions,” the assessment said.

Ukraine’s military has blown up bridges to force the Russians to build pontoon bridges, a tactic that has proven effective — and costly for the Russian army. Military forces are particularly vulnerable to artillery strikes as they congregate soldiers, armored vehicles and equipment while attempting a crossing.

In the first month of the war, the Ukrainians destroyed dozens of Russian armored personnel carriers in one location on the Irpin River, northwest of the capital, Kyiv, where the Russian military attempted seven unsuccessful pontoon crossings before retreating.

In the battle for control of the eastern coal-mining region known as the Donbas, Russian forces have attempted several pontoon crossings of the Seversky Donets, seen as an important tactical step toward the goal of surrounding a pocket of Ukrainian troops in and around the city of Sievierodonetsk.

On May 11, Ukrainian artillery struck a pontoon crossing with devastating effect, destroying the bridge, incinerating armored vehicles on both river banks and killing more than 400 soldiers, according to estimates by Western military analysts. The British Defense Ministry has issued statements corroborating, based on satellite imagery, Ukrainian accounts and aerial drone imagery posted online of the strike.

The 650-mile-long Seversky Donets River originates in Russia and meanders southeast through the Donbas region before re-entering Russian territory, forming oxbow lakes, floodplains and swamps that are an effective barrier for Russian armored vehicles. Still, Russia has gained some ground in its eastern offensive in incremental advances and repeated attempts to storm Ukrainian lines, under the cover of intense artillery bombardments.