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IZYUM, Ukraine - Ukrainian military forces were massing on the outskirts of Slovyansk Wednesday, fortifying positions as fears grew that violent clashes with pro-Russian separatists could escalate.

At the town of Izyum, about 30 miles northwest of Slovyansk, at least four helicopters had landed in a field alongside 17 other military units and special forces personnel.

Ukrainian Army troops receive munitions at a field on the outskirts of Izyum, Eastern Ukraine, on April 15, 2014.Sergei Grits / AP

The buildup of forces blocked the main road between Donetsk and Kharkiv, and there were reports of a shooting in nearby town of Kramatorsk.

Despite fears of a possible imminent assault by Ukrainian troops, the Slovyansk appeared calm, the Associated Press reported.

Pro-Russian insurgents dug in Tuesday across eastern Ukraine, fortifying positions around seized buildings and erecting new barricades.

It came as the United Nations warned that misinformation, propaganda and incitement to hatred are causing tensions in eastern Ukraine that could lead to the region breaking away like Crimea.