ZAPORIZHZHIA, Ukraine — The chief of the general staff of the Russian military, Gen. Valery Gerasimov, the country’s highest ranking uniformed officer, made a visit to dangerous front-line positions in eastern Ukraine late last week in an effort to “change the course” of Russia’s flagging offensive there, according to a senior Ukrainian official. Two U.S. officials with knowledge of the visit also backed that assessment.

Ukrainian officials learned of the visit, the Ukrainian official said, but not in time to catch General Gerasimov. When Ukrainian forces launched an attack on one position visited by General Gerasimov, at School No. 12 in the Russian-controlled city of Izium on Saturday evening, he had already departed for Russia. Still, some 200 soldiers, including at least one general, were killed, the Ukrainian official said, speaking on condition of anonymity to discuss a sensitive military operation.

Two U.S. officials, who spoke on condition of anonymity to discuss confidential intelligence assessments, confirmed that General Gerasimov had been in eastern Ukraine for the past couple days, but had no information about the attack on the Russian base. The Russian Defense Ministry did not immediately respond to a request for comment.

“Our working assumption is that he was there because there’s a recognition they haven’t worked out all their problems yet,” said one of the officials.

The presence of such a high-ranking official on the front lines is highly unusual and comes amid what Western military analysts describe as increasing disarray within Russian forces. Even with dramatically scaled down objectives, Western officials and analysts say the Russian military continues to struggle with logistical problems and coordination among its troops, while facing persistently fierce resistance from the Ukrainians.

Izium, a medium-sized city in eastern Ukraine, has become a base of operations for the Russian military as it pursues an offensive meant to wrest away the two eastern Ukrainian territories bordering Russia that make up the region known as the Donbas. The successful seizure of the area would represent a consolation prize for the Kremlin, after an embarrassing withdrawal from the region around the Ukrainian capital, Kyiv, which, according to U.S. intelligence assessments, the Russian leadership had expected to fall within days of invasion.

But even in the east progress has been slow. Russian forces have been able to make incremental gains, day by day, taking some villages, while losing others, as strongly entrenched Ukrainian troops put up stalwart resistance.

General Gerasimov sits at the right hand of Russia’s president, Vladimir V. Putin, and is one of only three people, along with the president and the minister of defense, who were principally in charge of plotting the course of the war from its outset. This strict hierarchy that defines Russia’s military leadership is one reason Western analysts say Russia’s forces have so often appeared unable to adapt quickly to changing battlefield conditions.

For more than a month after the war started, Russian forces lacked a battlefield commander who might guide the action from inside Ukraine, leading to poor coordination among different units and services that has contributed to the deaths of thousands of troops. It also led to the deaths of 10 or more generals who had moved into front-line positions to try to untangle the mess.

Early last month, the Kremlin finally appointed a seasoned commander, Aleksandr V. Dvornikov, who was accused of ordering airstrikes on civilian neighborhoods in Syria, to oversee forces on the ground in Ukraine.

American officials said General Gerasimov’s secret visit to the eastern front underscores the problems Russian forces are confronting in the Donbas.

“It likely means things are not going well for the Russians,” Representative Jason Crow, a Colorado Democrat on the House Armed Services Committee and former Army Ranger, said in a telephone interview from Poland after visiting Ukraine on Saturday with Speaker Nancy Pelosi.

“They’ve had thousands killed in action, troop morale is low, and, very significantly, their offensive in the south and east appears to be stalled,” Mr. Crow said.

General Gerasimov had been in eastern Ukraine for several days and arrived on Saturday during the day at School No. 12, which was being used as a base by Russia’s Second Combined Arms Army, as well as airborne forces deployed to the region, the senior Ukrainian official said. According to preliminary information gathered by Ukrainian forces, Maj. Gen. Andrei Simonov, who was among the commanders at the base in Izium, was killed in the attack.

“The decision to destroy this object was taken not because of Gerasimov, but because it is an important base of operations,” the official said.