May was a particularly deadly month for the Russian army in Ukraine, with an average of more than 1,000 of its soldiers injured or killed each day, according to U.S., British and other Western intelligence agencies.

But despite its losses, Russia is recruiting 25,000 to 30,000 new soldiers a month — roughly as many as are exiting the battlefield, U.S. officials said. That has allowed its army to keep sending wave after wave of troops at Ukrainian defenses, hoping to overwhelm them and break through the trench lines.

It is a style of warfare that Russian soldiers have likened to being put into a meat grinder, with commanding officers seemingly oblivious to the fact that they are sending infantry soldiers to die.

At times, this approach has proved effective, bringing the Russian army victories in Avdiivka and Bakhmut in eastern Ukraine. But Ukrainian and Western officials say the tactics were less successful this spring, as Russia tried to take land near the city of Kharkiv.

American officials said that Russia achieved a critical objective of President Vladimir V. Putin, creating a buffer zone along the border to make it more difficult for the Ukrainians to strike into the country.

But the drive did not threaten Kharkiv and was ultimately stopped by Ukrainian defenses, according to Western officials.