From Reuters:

Ukrainian military spokesman Andriy Lysenko said on Tuesday that Russian Mi-24 helicopters had attacked a border post in Luhansk region the previous day, killing four border guards.
“Yesterday, during the day, at the border post of Krasnatalovka, Russian Mi-24 helicopters attacked Ukrainian border guards. As a result of the attack, four guards were killed, three were injured,” Lysenko told Reuters.

The news comes as Russian president Vladimir Putin and Ukainian president Petro Poroshenko meet in Minsk, Belarus for talks on the ongoing conflict. It also follows Ukraine’s capture of ten Russian paratroopers yesterday at a site 15 miles into Ukraine from the Russian border.