In a significant boost to Ukraine’s efforts to quell a rebellion that has split the nation, government forces on Saturday cleared pro-Russian separatists out of a key rebel stronghold in the east after several days of fierce battles, Ukrainian officials and rebels said.

The recapture of Slovyansk marks a major step for the Kiev government, which has struggled for months to contain a separatist rebel movement that has captured government buildings and cities in the east. Slovyansk had been the site of some of the most intense fighting, and until Saturday, it had appeared to be one of the cities most firmly in rebel hands.

Ukrainian leaders were jubilant Saturday — President Petro Poroshenko ordered the hoisting of the blue-and-yellow Ukrainian flag above Slovyansk’s city hall, while Russian officials did not directly respond to rebels’ requests for aid. Russian President Vladimir Putin has promised to defend the interests of Russians wherever and whenever they come under attack, but he has left open the question of whether that extends to an outright invasion of eastern Ukraine.

It was unclear whether the capture of Slovyansk marked a decisive turning point in the battle against the separatists, but it appeared to be one of the first times the poorly equipped Ukrainian army has forced the rebels into a major retreat. The fight escalated after a cease-fire expired Monday, with Ukrainian forces using airstrikes and artillery bombardment to hit rebel positions. Rebels, meanwhile, have shot down Ukrainian planes.

“This is not a complete victory. But the cleansing of Slovyansk from armed-to-the-teeth gangs of animals has great symbolic importance,” Poroshenko said, vowing that the military would soon “liberate” the rest of the rebel-held territories, as well, and promising both humanitarian aid and legal amnesty to civilians in recaptured areas.

1 of 74 Full Screen Autoplay Close July 17, 2014 Thursday July 16, 2014 Thursday July 15, 2014 Thursday July 14, 2014 Thursday July 11, 2014 Thursday July 10, 2014 Thursday July 9, 2014 Wednesday July 8, 2014 Tuesday July 7, 2014 Monday July 3, 2014 Thursday July 1, 2014 Tuesday Skip Ad × Fighting sweeps eastern Ukraine View Photos Military launches air and artillery strikes against separatists after President Petro Poroshenko suspended a 10-day cease-fire that had failed to bring tranquility to the country. Caption Fighting raged in Ukraine’s east on July 16 when separatists tried to break through the lines of government forces near the border with Russia and a tentative step toward agreeing on conditions for a cease-fire failed. July 18, 2014 Residents look at Ukrainian servicemen patroling in vehicles near the eastern Ukrainian city of Kramatorsk. Fighting in Slovyansk ended after separatist militia fled the city on July 5 in the face of a Ukrainian army advance. The United States built a case that pro-Moscow separatists downed a Malaysian airliner in Ukraine with a surface-to-air missile, killing all 298 people on board — with the possible technical assistance of Russians. Genya Savilov/AFP/Getty Images Buy Photo Wait 1 second to continue.

“This is the beginning of the fight with militants for the territorial integrity of Ukraine,” Poroshenko said. He warned, however, that there are still quite a lot of trials ahead.”

Government officials announced they had recovered weapons in Slovyansk left behind by fleeing militants, including a tank.

“The terrorists are losing, surrendering,” Interior Minister Arsen Avakov wrote on Facebook. The Ukrainian military said that two Ukrainian servicemen had died and that 13 were injured.

Some rebel leaders denied the significance of the retreat, saying it was carried out only to protect civilians.

“Ukrainian forces were trying to level Slovyansk to the ground,” Andrei Purgin, a top separatist leader, told the Interfax news service. “What would you do, if you were being thrashed by mortars, artillery weapons, being bombed from the air — and you had three tanks and machine guns?

“The departure of militias from Slovyansk is a commonplace step to protect civilians from death,” Purgin said. “Our resistance is not broken.”

Slovyansk was a base for Igor Girkin, a rebel commander and Russian citizen also known by his nom de guerre Igor Strelkov, who posted a YouTube video on Friday pleading for Russia to send military aid because separatists in Slovyansk were on the verge of collapse.

On Saturday, high-ranking rebels described the pro-Russian losses as “minimal” and Girkin’s withdrawal from Slovyansk as a planned move.

“Kutuzov also departed — and this was the plan,” said Pavel Gubarev, the self-proclaimed “People’s Governor” of the Donbas region, likening Girkin to the Russian general who defeated Napoleon and suggesting the rebels were simply regrouping. “In general, Russians depart only before a decisive, victorious battle.”

Still, Denis Pushilin, the leader of the self-proclaimed Donetsk People’s Republic, publicly voiced frustration Saturday, suggesting that the Slovyansk militias had been let down by their Russian patrons.

“What to say. They encouraged us. Encouraged us and abandoned us,” Pushilin wrote on Twitter. “Putin’s words about protecting the Russian people, protecting Novorossiya, they were beautiful. But they were only words,” he said, using a historical term for a band of the former Russian Empire that includes parts of Ukraine.

By Saturday night, pro-Russian militias had also left the nearby city of Kramatorsk, which they had admitted they found “awkward to defend,” according to separatist leaders quoted by RIA Novosti. Ukrainian forces raised the state flag in victory there, as well.

In the city of Donetsk, also a rebel stronghold for the past several months, news of the Ukrainian military’s gains in Slovyansk inspired panic Saturday, as residents feared similar battles between government and pro-Russian forces would erupt around them.

The mayor of Donetsk, Alexander Lukyanchenko, acknowledged periodic firing around the airport and the recent arrival of retreating rebels, but encouraged residents to stay calm.

Rebels also called Saturday for a resumption of peace talks brokered by Russia and the Organization for Security and Cooperation in Europe. Poroshenko had suggested a day earlier that such talks could take place as early as Saturday, but the two sides never reached agreement on where to hold them, and on Saturday the government did not renew calls for talks.

Meanwhile, the Russian Foreign Ministry called for a U.N. inquiry into the “murder” of civilians in the regions of Donetsk and Luhansk. It also said Russia would stop returning Ukrainian military materials left in Crimea until there was peace in eastern Ukraine.

Russia has been slowly handing over materiel that Ukrainian forces left behind in Crimea since the Kremlin annexed the territory in March, shortly after Ukrainian protesters ousted Russian-friendly president Viktor Yanukovych.

In April, pro-Russian separatists started capturing territory in eastern Ukraine. The bloody conflict has killed hundreds and displaced tens of thousands, according to U.N. estimates.

Michael Birnbaum in Brussels contributed to this report.