The situation in the area of the anti-terrorist operation remains stable, however the insurgents are building up their forces, spokesman for the Information and Analytical Center of the National Security and Defense Council Andriy Lysenko has said.

"The sides largely adhere to the ceasefire. This is the first relatively calm day in the east of Ukraine," Lysenko said at a briefing in Kyiv on Tuesday.

At the same time, the militants are building up their presence in the immediate vicinity of a National Guard checkpoint near the town of Slovianoserbsk, the spokesman said.

"At the moment, ten T-72 tanks are concentrated in the vicinity of the checkpoint. The Ukrainian military are reinforcing their position and are not reacting to provocations," Lysenko said.