Russian President Vladimir Putin on Saturday ordered the border service to reinforce the state border with Ukraine, the Kremlin press service told Russian news agencies.

Russian President Vladimir Putin on Saturday ordered the border service to reinforce the state border with Ukraine, the Kremlin press service told Russian news agencies.

Putin issued the order for border guards to take all necessary measures to prevent illegal crossings, Russian news agencies reported.

Kiev said Thursday that it had abandoned three border posts neighboring Russia in the volatile Lugansk region of eastern Ukraine after attacks by separatists.

It has also said that fighters are entering Ukraine frequently from Russia, some having travelled from the North Caucasus region.

Russian Prime Minister Dmitry Medvedev said Thursday that thousands of Ukrainians are fleeing the combat zone into bordering Russian regions and 4,000 have sought refugee status.