Ukraine has closed several crossing checkpoints on the border with Russia in its eastern Lugansk region, the State Border Service said Thursday.

Ukraine has tightened measures on its border due to the "unstable security situation" in the region, the press service of the agency said in a statement.

Authorities have also evacuated guard staff from the closed crossing checkpoints over "threats to their life" triggered by the frequent attacks by rebel forces, the statement said.

Ukrainian authorities have officially informed the Russian Federation about the closure of several border crossing checkpoints, the statement said, without specifying the number of border posts that were affected.

The move came after fierce battles on the Ukraine's eastern frontier between border guards and separatist insurgents, which left at least eight people dead.

Violent clashes between Ukrainian government troops and armed activists are underway in Lugansk and its neighboring Donetsk regions since early April, after insurgents established "people's republics" in their regions, seeking independence from Kiev.