BUCHA, Ukraine — The Russian forces that were intent on overwhelming Kyiv at the war’s start with tanks and artillery retreated under fire across a broad front on Saturday, leaving behind them dead soldiers and burned vehicles, according to witnesses, Ukrainian officials, satellite images and military analysts.
The withdrawal suggested the possibility of a major turn in the six-week war — the collapse, at least for now, of Russia’s initial attempt to seize Kyiv, the Ukrainian capital, and the end of its hopes for the quick subjugation of the nation.
Moscow has described the withdrawal as a tactical move to regroup and reposition its forces for a major push in the Donbas region of eastern Ukraine. While there are early indications that the military is following through on that plan, analysts say it cannot obscure the magnitude of the defeat.
“The initial Russian operation was a failure and one of its central goals — the capture of Kyiv — proved unobtainable for Russian forces,” Michael Kofman, the director of Russian studies at C.N.A., a research institute in Arlington, Va., said in a telephone interview Saturday.
Elsewhere in Ukraine, Russian attacks continued unabated, and the Pentagon has cautioned that the formations near Kyiv could be repositioning for renewed assaults.
In the south, an aid convoy organized by the International Committee of the Red Cross that had stalled on its way to bring some relief to the besieged city of Mariupol was on the move again. The hope, repeatedly frustrated by Russian shelling, was to bring emergency supplies to trapped residents and to evacuate hundreds of those who have endured weeks of bombardment that has left shortages of food and water.
In the suburban towns north of Kyiv, the Ukrainian army was advancing through a tableau of destruction, with dozens of wrecked tanks on streets, extensive damage to buildings and the bodies of civilians still lying uncollected. Kyiv and its surroundings, which had echoed with artillery booms and gunfire for weeks, had gone quiet.
Ukraine’s military on Saturday moved into Bucha, a key town on the west bank of the Dnipro River — which divides Kyiv — days after Russian forces had sacked it on their way out.
“They went from apartment to apartment collecting televisions and computers, loaded them on their tanks and left,” Svetlana Semenova, a retiree, said of the Russian departure, which she described as chaotic. “They left in a hurry.”
A few dozen people who had been living mostly in basements for a month staggered outside to collect food — bags of potatoes and bread — brought by Ukrainian soldiers.
Elena Shur, 43, an accountant for Ukraine’s national airline, said the first sign of the Ukrainian military came on Friday, when a civilian car carrying soldiers drove through town waving the country’s flag.
“We saw people on the street, and soldiers,” Ms. Shur said. “I cried.”
Reporters counted six bodies of civilians on the streets and sidewalks of Bucha. It was unclear under what circumstances they had died, but the discarded packaging of a Russian military ration was lying beside one man who had been shot in the head.
The town was the site of a major Ukrainian ambush of a Russian armored column in the first days of the war, and one street was blocked by dozens of incinerated tanks and trucks.
Despite that setback, the Russians had captured Bucha and held it for about a month. They executed half a dozen members of the Territorial Defense Force — the volunteer army many Ukrainians joined when the war started — leaving the bodies in a heavily mined part of town, said Varvara Kaminskaya, 69.
The Ukrainians have advanced at least another 15 miles to the northwest of Bucha, where they now fly Ukrainian flags over former Russian checkpoints.
After their initial assault on the capital failed, the Russian army had dug into defensive positions outside of Kyiv, suggesting an intention to hold a front line near the city. In an artillery war, trenches afford soldiers the best chance of survival.
Those were abandoned in and around Bucha on Saturday. On the northern edge of town were the abandoned berms that had sheltered Russian artillery emplacements, surrounded by green boxes and hundreds of empty shell cases.
“According to our information, they are running away from all areas around Kyiv,” said Sgt. Ihor Zaichuk, the commander of the 1st company of the 2nd Azov battalion in the Ukrainian army, which fought in Bucha.
“They can say on their own television stations, if they want, that they are the second most powerful army in the world,” he said. “But they aren’t anymore.”
He cautioned, however, that the Russians might return. “Only their commanders know if they will be re-equipped and return.” Even as cars lined up on some roads, making their way back into Kyiv, workers were building new defenses from heavy logs.
On the east bank of the Dnipro, Ukrainian forces were pressing forward in villages dozens of miles from the capital, according to an intelligence officer with the S.B.U., the Ukrainian domestic intelligence service, who declined to be identified for security reasons.
Analysts said that Moscow’s stated decision to refocus its military on the Donbas in eastern Ukraine is likely to be accurate, but mostly because they had little option.
“The Russians are adjusting their goals to reality,” Lawrence Freedman, emeritus professor of war studies at King’s College London, said in an interview on Saturday. “I think they know they’re in trouble, so I don’t think it’s a ruse to say they’re concentrating on the Donbas, because in reality that’s all they can do.”
Mr. Kofman, the expert on the Russian military, said the Russian army had lost about 2,000 pieces of equipment that was either destroyed, captured or abandoned, including about 350 tanks.
As the Russians retreated, they left mines and booby traps behind in an effort to slow the Ukrainians’ pursuit, according to Ukrainian officers in different towns. In the suburb of Irpin, which the Ukrainians had recaptured before Bucha, demining operations were in full swing on Saturday. Some civilian bodies had been booby-trapped to kill emergency workers, Ukrainian officials said.
One group of military engineers, dressed in heavy blue Kevlar armor, had tied a rope to a body. They pulled on it, to see if the motion would trigger booby traps. By late in the day, however, the body remained there, with the engineers apparently unable to ascertain if it was safe to collect.
In the village of Dmytrivka, west of the capital, there were signs of a hasty Russian retreat from a scene of carnage. On a forest road leading out of the village, nine tanks and armored vehicles lay destroyed and gutted by fire, the detritus of a tank battle three days earlier. The turrets and heavy guns of two tanks lay tossed aside. Inside one armored personnel carrier, the burned human remains of men were visible.
Valentina Yatsevich, 58, a villager walking past the wrecks toward her home, said, “They did not leave, they were destroyed.”
In Russia itself, the retreat caused consternation among the war’s cheerleaders, with state television having previously raised expectations that the Russian military would capture Kyiv.
Semyon Pegov, a popular pro-Kremlin war blogger embedded with the Russian troops, posted a video to the social messaging app Telegram on Saturday describing the move as “a withdrawal, not a flight.”
The retreat was necessitated, he said, by Russia’s stretched-out supply lines and the threat of further losses as its troops tried to survive in field conditions facing a much better supplied and fortified enemy.
It was an effort, mirrored by other pro-Kremlin outlets, to explain why Russia seemed to have sharply scaled back its war aims in recent days, after taking painful losses in fighting for the Kyiv suburbs.
Russian hard-liners calling for an assault on Kyiv saw the retreat as a disappointment. “I don’t know why this decision was made,” Aleksandr Kots, a war correspondent for the Russian tabloid Komsomolskaya Pravda, wrote on Telegram. “The war is only beginning. We’ll figure out later who was right and who was at fault.”
The Kremlin maintained its defiance as state television released an interview with Dmitri S. Peskov, Mr. Putin’s spokesman, characterizing the United States as being at the root of Europe’s ills. He expressed confidence that European countries would renew relations with Russia once they “sober up a little from the American bourbon.”
In Lithuania, President Gitanas Nauseda announced that his country would no longer import Russian gas starting this month. “If we can do it, the rest of Europe can do it too,” he wrote on Twitter. The European Union is looking for ways to reduce Europe’s dependency on Russian oil and gas.
In other developments on Saturday, Pope Francis, visiting the Mediterranean island nation of Malta, edged closer to blaming President Vladimir V. Putin of Russia for the war in Ukraine than he had before. In an address to Maltese dignitaries and officials, the pope blamed a “potentate, sadly caught up in anachronistic claims of nationalist interests” for casting “dark shadows of war” from Europe’s east.
Francis has declined to explicitly blame Mr. Putin or Russia as the aggressor for various reasons, including the Vatican’s hopes of playing a role in a potential peace agreement. But on Saturday, he clearly seemed to be speaking about Mr. Putin, who he said was “provoking and fomenting conflicts.”
Andrew E. Kramer reported from Bucha, Ukraine, and Neil MacFarquhar from New York. Reporting was contributed by Anton Troianovski in Istanbul; Carlotta Gall in Dmytrivka, Ukraine; Megan Specia in Warsaw; Steven Erlanger in Brussels; Maria Varenikova in Bucha, Ukraine; and Jason Horowitz in Rome.