Ukraine previously pledged to beef up control of its leaky border after accusing the Kremlin of pouring arms and fighters across it to fuel three months of brutal fighting between pro-Russian rebels and government force.

But this time the illicit goods were being herded in the other direction after unknown thieves raided a farm in the Bilovodsk district overnight and trampled a path to the border, Lugansk police spokeswoman Tetyana Pogukay wrote on Facebook.

One errant heifer apparently strayed from the group and was found around a kilometre (half a mile) from the frontier, the post said.

According to Ukrainian agricultural experts cows can go for as much as $1000 (740 euros) each in the region.

Tensions along the volatile border between the two ex-Soviet states are at boiling point after Ukraine on Thursday accused a Russian airforce jet of shooting down one of its warplanes.