KIEV, Ukraine — Government forces made a major advance Saturday in a nearly three-month fight against pro-Russian militants, raising the national flag back over the city of Slovyansk in eastern Ukraine.

“Mr. President, the order to liberate Slovyansk has been fulfilled,” Defense Minister Valery Geletey reported to President Petro Poroshenko in a statement posted on the presidential website on Saturday. “This very moment the state banner of Ukraine was raised over Slovyansk city council in front of a line-up of Ukrainian soldiers.”

Poroshenko, in televised remarks, said “it is not a complete victory.”

“But the liberation of Slovyansk from the armed-to-the-teeth gang of subhumans has a tremendous symbolic importance,” the president said. “It is the beginning of a breakthrough in the struggle with the militants for the territorial integrity of Ukraine.”

Slovyansk, an industrial center of 100,000 people in the coal-mining Donetsk region, was captured by gunmen on April 12, a move shortly followed by similar raids in dozens of other cities and towns of eastern Ukraine, including the regional capital cities of Donetsk and Luhansk.

The militants distributed firearms to local sympathizers, formed what they called People’s Republics of Donetsk and Luhansk and demanded Russia recognize and annex them the way it annexed Ukraine’s Crimea peninsula in mid-March.

Despite appeals by the rebels, Russia balked at recognizing the self-proclaimed republics and did not send in the thousands of troops it had amassed just across the border.

Last month Russian President Vladimir Putin, facing economic sanction measures from Western nations, asked Parliament to revoke its earlier permission to use troops in Ukraine.

Donetsk region self-proclaimed parliament head Denis Pushilin publicly accused Putin on Saturday of having reneged on supporting the pro-Russians’ cause.

“They instilled hope in us but they deserted us,” Pushilin wrote Saturday on his Twitter account. “Putin’s words about protecting Russian people were beautiful but those were just words.”

Another pro-Russian rebel leader, former Russian army colonel and self-proclaimed defense minister of Donetsk Republic Igor Strelkov, also criticized Russian leaders.

“If Russia doesn’t achieve an immediate ceasefire or doesn’t deploy its armed forces to protect the Russian people we will be destroyed within a week or maximum of two weeks,” Strelkov said in a video statement posted on Facebook.

Friday night, rebel forces surrounded in Slovyansk and led by Strelkov made a desperate attempt to break through and leave the city, Ukraine’s Interior Minister Arsen Avakov wrote on Facebook.

“They are on the run!” he wrote. “A significant part of rebels have run away from Slovyansk. Terrorists are sustaining losses and surrendering.”

Dmitry Tymchuk, a leading Ukrainian defense expert, called the events a major military breakthrough but warned against excessive elation.

“This is a very serious victory which may be a huge step toward ending the war,” Tymchuk said. “The rebels are retreating now toward the regional capital of Donetsk and they may succeed in turning it into a real armed fortress if Russia continues to supply them with weapons and hardware.”