On Wednesday night, roughly 300 pro-Russian separatists attacked a Ukraine military unit in Mariupol, a Black Sea port city in the southeast. Ukrainian troops returned fire, killing three and wounding 13. None of the Ukrainian troops were wounded, according to local officials, who reported 63 arrests. Mariupol is one of the locations where separatists have seized government buildings. Meanwhile, Russian President Vladimir Putin warned Ukraine of “the abyss they’re heading into” in eastern Ukraine, and dismissed reports that Russia is operating in the region.