An armed supporter of the self-proclaimed Donetsk People's Republic stands guard at a newly erected barricade on a road which leads to an airport in Donetsk. Reuters

Heavy fighting broke out in the disputed Donetsk region of eastern Ukraine Monday, with Ukrainian military forces launching an assault in an attempt to retake control of the region where Malaysia Airlines Flight MH17 crashed Thursday.

A Ukrainian spokesman told reporters that the military had captured the Donetsk airport. Exact numbers are difficult to pin down, but sources on the ground have said that approximately four civilians were killed during the fighting Monday.

“The active stage of the counter-terrorist operation continues,” Vladislav Seleznev told CNN Monday. “The government is now at full control of the airport and the road leading to it.”

The city council warned residents, who have seen their city the subject of international headlines since Russian-backed separatists invaded the region months ago, to remain indoors for their own safety.

“The bus station is closed. Car movement is limited. A nine-story residential building at the train station area has been damaged. A market outside the train station caught on fire as the result of artillery fire. Still, the train is working,” an advisory warned.

The Kiev-based government denied that Ukrainian troops had been deployed to Donetsk, a separatist stronghold since Kremlin-backed fighters seized the city in April, but did say a “self-organized” group was fighting rebels.

“There is work on clearing approaches to the city, on destroying checkpoints of the terrorists. If there are explosions in the middle of the city, then it is not Ukrainian soldiers,” spokesman for Ukraine’s national security council spokesman Andriy Lysenko told the Guardian. “We have strict orders not to use air strikes and artillery in the city. If there is fighting in the city, we have information that there is a small self-organized group who are fighting with the terrorists.”

Yet the council seemed to contradict itself with a tweet sent out shortly after initial denials, saying “[Anti-terror operation] forces sealing ring around Gorlovka, Donetsk. Also expanding zone of control around Donetsk airport.”

Intermittent clashes were highlighted by smoke plumes rising from the center of the city, which is home to nearly one million people and located 40 miles (60 km) from the site of the heart-wrenching Malaysia Airlines disaster. Government officials denied any civilians had been killed, although journalists covering the unfolding events reported witnessing one artillery shell fall in a residential courtyard, whereupon it exploded, knocked out the windows of nine floors and destroyed parked cars. Two men and one woman are believed to have been killed in that incident.

Ukrainian President Petro Poroshenko ordered a ceasefire in for the 24 mile (40 km) radius around the crash site, a mandate that does not include Donestk.

The seeds of the current unrest were laid when Poroshenko’s predecessor, former Ukrainian President Viktor Yanukovych, turned his back on a trade agreement with the European Union, instead opting to align Ukraine closer to Russian interests. The shift unleashed widespread protests throughout Ukraine, leading to Yanukovych’s exit, Russia’s annexation of Crimea, a rebellion fanned by the Kremlin, and the MH17’s crash last week, thought to be the fault of pro-Russian separatists.