LONDON (MarketWatch) -- A Ukrainian helicopter was shot down over the eastern city of Slovyansk, according to the country's defense ministry, as fighting in the area escalated. Machine gunfire brought down a Ukrainian Mi-24 helicopter at about 2:30 p.m. local time, the defense ministry said in a statement on its website. The "pilots are undamaged," and were evacuated, the government said. Earlier Monday, Ukrainian authorities said heavy fighting that broke out in Sloyvansk, a stronghold of pro-Russian separatists, left four Ukrainian soldiers dead, while a rebel commander said more than 20 militants had possibly been killed.