Ukraine targeted pro-Russia separatists who’ve fallen back to two of the nation’s biggest eastern cities, stepping up a four-month military offensive in the wake of last week’s Malaysia Air plane disaster.

Government troops seized towns in the Donbas region and took over part of Donetsk, according to a Defense Ministry statement today on Facebook. The army has begun an “advance across all fronts,” Alexander Borodai, prime minister of the self-proclaimed Donetsk People’s Republic, told reporters.

“The time has come when Russia must take a final decision — to really support Donbas’s Russians or abandon them forever,” rebel commander Igor Strelkov said on his page on Russian-language social media website Vkontakte.

After pushing them out of bases in the cities of Slovyansk and Kramatorsk, Ukraine’s government is intensifying its assault on the separatists, whose appeals for Russian intervention haven’t been met. The heightened military campaign comes days after a missile downed MH17, killing all 298 people on board.

Nations including the U.S and the U.K. say the rebels probably fired the missile. Russian President Vladimir Putin says Ukraine is to blame because it ended a cease-fire with the rebels last month. Putin will tomorrow host a meeting to discuss “matters related to ensuring the sovereignty and territorial integrity of the Russian Federation,” the Kremlin said today in an e-mailed statement.

While the insurgents repelled tanks near the city of 1 million, Ukraine’s forces have an “enormous” technical advantage, according to Borodai, who said he’s seeking a resumption of cease-fire talks. The army deployed warplanes and fired Grad missiles in Donetsk’s outskirts, he said.

Gunfire was heard in “many parts” of Donetsk this morning and there was shelling near the airport, the city council said on its website, without providing details of casualties. At 1 p.m. local time, plumes of thick black smoke could be seen rising from the outskirts.

“The Ukrainians have just bombed the market near the main train station and also hit a residential building,” said Viktor Nechaevsky, who works at the press service of the Donetsk People’s Republic. “There are victims.”