Russia has blocked Ukraine-registered trucks from entering its territory, in a tit-for-tat response to expanding efforts by Ukraine activists to block Russian transit from crossing into or leaving Ukraine.
The Russian move, ordered Sunday by the Transit Ministry, follows a push in several Ukrainian regions last week to block Russian cargo transit at its borders.
Russian news outlets quote transit officials as saying more than 100 Russian trucks are currently blocked in different regions of Ukraine.
Officials say more than 500 other trucks headed for Russia from European Union countries are either unable to enter Ukraine from the west or to return home from deliveries in Russia since the Ukraine blockade began.
Both sides imposed a series of food product import and air traffic bans, as tensions rose and armed conflict in eastern Ukraine erupted two years ago after the Russian parliament annexed Ukraine's Crimea Peninsula.
International monitors say more than 9,000 people have been killed since Russian-backed rebels in Russian-speaking eastern Ukraine took up arms against the Kyiv government in April 2014.
Fighting has largely subsided in recent months, but neither side has fully implemented the so-called Minsk cease-fire pact negotiated last year by envoys from Europe, Russia and Ukraine.