Fighting broke out near the railway station at the heart of Ukraine’s Donetsk on Monday, July 21, in what pro-Russia armed groups said was an attempt by government forces to seize back the east city, according to Reuters.

The government in Kiev denied sending the regular army into the center of Donetsk, but said small “self-organized pro-Ukrainian groups were fighting the pro-Russian rebels in the city.”

Four people were killed in clashes near the railway station and close to the airport outside Donetsk, local health officials said in the industrial city which was home to about 1 million people before many fled the fighting in the region.