Russia is preparing to step up its attacks on Ukraine using Iranian-made exploding drones, according to Ukraine’s president, as Moscow looks for ways to keep up the pressure on Kyiv after at least 63 Russian soldiers were killed in an attack in the latest battlefield setback for the Kremlin’s war strategy.

“We have information that Russia is planning a prolonged attack by Shaheds (exploding drones),” President Volodymyr Zelenskyy said in his nightly video address late Monday.

He said the goal is to break Ukraine’s resistance by “exhausting our people, (our) air defense, our energy,” more than 10 months after Russia invaded its neighbor.

Russian President Vladimir Putin appears to be exploring ways to regain momentum in his flawed war effort, which in recent months has been undermined by a Ukrainian counteroffensive backed by Western-supplied weapons. That has brought sharp rebukes in some Russian circles of the military’s performance.

In the latest embarrassment for the Kremlin, Ukrainian forces fired rockets at a facility in the eastern Donetsk region where Russian soldiers were stationed, killing 63 of them, according to Russia’s Defense Ministry. Other, unconfirmed reports put the death toll much higher.