The Ukrainian State Border Service has tightened border control and restricted arrivals of foreign citizens, first and foremost male Russian citizens aged from 16 to 60, agency head Petro Tsyhykal said.

"Checkpoint control has been tightened. The arrivals of foreign citizens, above all citizens of Russia, have been restricted. There is no admittance of male Russian citizens aged from 16 to 60," Tsyhykal said at a meeting on heightening national defense levels, which was chaired by Ukrainian President Petro Poroshenko on Friday morning.

No restrictions have been imposed on Ukrainian citizens on the border, he said.

"Am I right that these measures are preventing Russia from forming private army units, which are actually composed of servicemen of the Russian Armed Forces, and from holding the operations they attempted to conduct in 2014?" Poroshenko asked. Tsyhykal gave an affirmative answer.

The president underlined the importance of tightening requirements on registration of Russian citizens especially in the regions where martial law is in effect.