Heavy fighting between Ukrainian forces and pro-Russian separatists has been reported in east Ukrainian Donetsk region, with the epicenter in Krasny Liman and nearby Yampil villages.
One military source quoted by the Reuters news agency said some 4,000 separatists had been involved while Ukrainian infantry were supported by some 20 tanks as well as artillery and heavy armor.
A top rebel commander, Igor Strelkov, reported "heavy losses" in equipment and arms among the separatists.
Fighting reportedly erupted early on June 19 after rebels refused to lay down their arms as part of President Petro Poroshenko's proposed peace plan.
It includes an offer of a unilateral cease-fire by government forces and amnesty for the separatists - but only if they lay down their weapons.